Sounds like corrupted preferences. If you search this forum you will find many many posts on this issue and how to find and rename/delete these preferences.
In Captivate 6 there's also a special .bat file utility at either of these folder locations:
C:\Program Files\Adobe\Adobe Captivate 6 x64\utils
C:\Program Files (x86)\Adobe\Adobe Captivate 6 (32 Bit)\utils
You just need to close down Captivate and execute this batch file to clean out your preferences ready for Captivate to recreate them on next launch.
