I'm now running into this problem too.
Yesterday, I put a DVD into my computer's optical drive to capture a few seconds of video. Now, whenever I start up OBS Studio and there's no disc in that DVD drive, it pops up this error message complaining that there's nothing in the drive. I have already removed the window capture source capturing the DVD player software. I have tried putting the disc in the drive, starting OBS, adding the source, removing the source, and closing OBS in various orders and haven't hit upon a combination that works. The error dialog goes away and OBS starts if I choose "continue" or "cancel" - it's only "retry" that prevents OBS from opening until if finds something in the drive. Still, I'd rather not see this error message multiple times a day.
I was surprised at this because OBS gracefully handles window sources that aren't running, cameras that aren't plugged in, and so on, and yet complains about a DVD drive that once had a disc in it and was connected to a source it was once told to capture. How can I tell OBS to stop doing this? Is there some file I can edit? I already tried installing an updated version of OBS, but it's still looking for a disc in the drive. I suspect this would be solved by a clean install of OBS, but I have many scenes and sources and I really don't want to wipe everything.