I have the same problem... Until the last week everything worked perfectly and I'm a huge fan from OBS Studio but now I Can't record... But I think you guys will fix that very fast :D
And I'm sorry for all my faults in this text, I'm not an english speaking Person :)
her is My log:
Completely ignored arguments: [--nativeLauncherVersion, 307]
[18:58:56] [Client thread/INFO]: Setting user: KabelWlan
[18:58:56] [Client thread/INFO]: (Session ID is <censored>)
[OptiFine] (Reflector) Method not present: afh.func_149713_g
[OptiFine] (Reflector) Class not present: net.minecraftforge.common.MinecraftForge
[OptiFine] (Reflector) Class not present: net.minecraftforge.common.ForgeHooks
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.MinecraftForgeClient
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.ForgeHooksClient
[OptiFine] (Reflector) Class not present: net.minecraftforge.fml.common.FMLCommonHandler
[OptiFine] (Reflector) Class not present: net.minecraftforge.fml.client.FMLClientHandler
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.IItemRenderer$ItemRenderType
[OptiFine] (Reflector) Method not present: anm.getSkyRenderer
[OptiFine] (Reflector) Method not present: anm.getCloudRenderer
[OptiFine] (Reflector) Method not present: anm.getWeatherRenderer
[OptiFine] (Reflector) Method not present: adm.countEntities
[OptiFine] (Reflector) Method not present: adm.getPerWorldStorage
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.IRenderHandler
[OptiFine] (Reflector) Class not present: net.minecraftforge.common.DimensionManager
[OptiFine] (Reflector) Class not present: net.minecraftforge.event.world.WorldEvent$Load
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.RenderItemInFrameEvent
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.GuiScreenEvent$DrawScreenEvent$Pre
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.GuiScreenEvent$DrawScreenEvent$Post
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.EntityViewRenderEvent$FogColors
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.EntityViewRenderEvent$FogDensity
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.EntityViewRenderEvent$RenderFogEvent
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.RenderLivingEvent$Pre
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.RenderLivingEvent$Post
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.RenderLivingEvent$Specials$Pre
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.RenderLivingEvent$Specials$Post
[OptiFine] (Reflector) Class not present: net.minecraftforge.fml.common.eventhandler.EventBus
[OptiFine] (Reflector) Class not present: net.minecraftforge.fml.common.eventhandler.Event$Result
[OptiFine] (Reflector) Class not present: net.minecraftforge.event.ForgeEventFactory
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.event.RenderBlockOverlayEvent$OverlayType
[OptiFine] (Reflector) Class not present: net.minecraftforge.event.world.ChunkWatchEvent$UnWatch
[OptiFine] (Reflector) Method not present: afh.getBedDirection
[OptiFine] (Reflector) Method not present: afh.isBed
[OptiFine] (Reflector) Method not present: afh.isBedFoot
[OptiFine] (Reflector) Method not present: afh.hasTileEntity
[OptiFine] (Reflector) Method not present: afh.canCreatureSpawn
[OptiFine] (Reflector) Method not present: afh.addHitEffects
[OptiFine] (Reflector) Method not present: afh.addDestroyEffects
[OptiFine] (Reflector) Method not present: afh.isAir
[OptiFine] (Reflector) Method not present: afh.canRenderInLayer
[OptiFine] (Reflector) Method not present: afh.getExtendedState
[OptiFine] (Reflector) Field not present: pk.captureDrops
[OptiFine] (Reflector) Field not present: pk.capturedDrops
[OptiFine] (Reflector) Method not present: pk.shouldRenderInPass
[OptiFine] (Reflector) Method not present: pk.canRiderInteract
[OptiFine] (Reflector) Method not present: akw.shouldRenderInPass
[OptiFine] (Reflector) Method not present: akw.getRenderBoundingBox
[OptiFine] (Reflector) Method not present: akw.canRenderBreaking
[OptiFine] (Reflector) Method not present: zw.onEntitySwing
[OptiFine] (Reflector) Method not present: zw.shouldCauseReequipAnimation
[OptiFine] (Reflector) Method not present: zw.getModel
[OptiFine] (Reflector) Method not present: zw.showDurabilityBar
[OptiFine] (Reflector) Method not present: zw.getDurabilityForDisplay
[OptiFine] (Reflector) Method not present: pf.isCurativeItem
[OptiFine] (Reflector) Method not present: aak.getRecordResource
[OptiFine] (Reflector) Method not present: bmv$b.preDraw
[OptiFine] (Reflector) Method not present: bmv$b.postDraw
[OptiFine] (Reflector) Class not present: net.minecraftforge.fml.common.asm.transformers.BlamingTransformer
[OptiFine] (Reflector) Class not present: net.minecraftforge.fml.relauncher.CoreModManager
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.model.ISmartBlockModel
[OptiFine] (Reflector) Class not present: net.minecraft.launchwrapper.Launch
[OptiFine] (Reflector) Class not present: net.minecraftforge.fml.client.SplashProgress
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.model.pipeline.LightUtil
[OptiFine] (Reflector) Class not present: net.minecraftforge.common.property.IExtendedBlockState
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.ItemModelMesherForge
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.model.ModelLoader
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.model.Attributes
[OptiFine] (Reflector) Class not present: mods.betterfoliage.client.BetterFoliageClient
[OptiFine] (Reflector) Class not present: net.minecraftforge.client.model.IColoredBakedQuad
[18:58:57] [Client thread/INFO]: LWJGL Version: 2.9.4
[OptiFine]
[OptiFine] OptiFine_1.8.8_HD_U_G7
[OptiFine] Fri Jan 27 18:58:58 CET 2017
[OptiFine] OS: Windows 10 (amd64) version 10.0
[OptiFine] Java: 1.8.0_25, Oracle Corporation
[OptiFine] VM: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
[OptiFine] LWJGL: 2.9.4
[OptiFine] OpenGL: GeForce GTX 970/PCIe/SSE2, version 4.5.0 NVIDIA 378.49, NVIDIA Corporation
[OptiFine] OpenGL Version: 4.0
[OptiFine] Maximum texture size: 16384x16384
[OptiFine] Checking for new version
[Shaders] ShadersMod version: 2.4.12
[Shaders] OpenGL Version: 4.5.0 NVIDIA 378.49
[Shaders] Vendor: NVIDIA Corporation
[Shaders] Renderer: GeForce GTX 970/PCIe/SSE2
[Shaders] Capabilities: 2.0 2.1 3.0 3.2 4.0
[Shaders] GL_MAX_DRAW_BUFFERS: 8
[Shaders] GL_MAX_COLOR_ATTACHMENTS_EXT: 8
[Shaders] GL_MAX_TEXTURE_IMAGE_UNITS: 32
[Shaders] Load ShadersMod configuration.
[Shaders] No shaderpack loaded.
[OptiFine] Version found: H6
[18:58:59] [Client thread/INFO]: Reloading ResourceManager: Default, KabelPack 2.0
[18:58:59] [Sound Library Loader/INFO]: Starting up SoundSystem...
[OptiFine] Loading textures/font/ascii.properties
[OptiFine] Loading textures/font/ascii_sga.properties
[18:58:59] [Thread-7/INFO]: Initializing LWJGL OpenAL
[18:58:59] [Thread-7/INFO]: (The LWJGL binding of OpenAL. For more information, see
http://www.lwjgl.org)
[18:58:59] [Thread-7/INFO]: OpenAL initialized.
[18:59:00] [Sound Library Loader/INFO]: Sound engine started
[OptiFine] Mipmap levels: 4
[OptiFine] Multitexture: false
[OptiFine] (Reflector) Field not present: bmx.field_110597_b
[OptiFine] Multipass connected textures: false
[OptiFine] ConnectedTextures: mcpatcher/ctm/default/0_glass_white/glass_pane_white.properties
[OptiFine] ConnectedTextures: mcpatcher/ctm/default/0_glass_white/glass_white.properties
[OptiFine] Multipass connected textures: false
[18:59:00] [Client thread/INFO]: Created: 512x512 textures-atlas
Overwrite output..
[LabyMod] Loading labymod..
[ModInfo] Downloading Modinfo..
[ModInfo] Downloading Cosmetics..
[UserCapes] Download all usercapes..
[LabyMod] The latest LabyMod version is v2.7.98, you are currently using LabyMod version v2.7.98
[LabyMod] You are using the latest version.
[LabyMod] New listener AccountManager
[AccountManager] Account KabelWlan has been load!
[18:59:01] [INFO] Loaded Mod AccountManager.desc
[18:59:01] [INFO] Loaded Mod ItemPhysic.desc
[LabyMod] LabyMod Version 2.7.98 for Minecraft 1.8.8 loaded!
[OptiFine] *** Reloading custom textures ***
[OptiFine] CustomColors: Colormap textures/colormap/grass.png
[OptiFine] CustomColors: Colormap textures/colormap/foliage.png
[OptiFine] CustomColors: Colormap mcpatcher/colormap/sky0.png
[OptiFine] CustomColors: Colormap mcpatcher/lightmap/world-1.png
[OptiFine] CustomColors: Colormap mcpatcher/lightmap/world0.png
[OptiFine] CustomColors: Colormap mcpatcher/lightmap/world1.png
Thank you for an answer
Greets KabelWlan