You can have any number of Captivate major versions installed on your PC and they don't usually interfere with one another. (I happen to have versions 3, 4, 5.0, 5.5, 6.1 on my laptop.)
Are you launching Cp6 using Run As Administrator?
If you had previously installed a trial version of Cp6, did you delete the Preferences folder before upgrading or installing 6.1? If not, then do so.
Sometimes Captivate crashes due to corrupted fonts. The usual debug process is to go to your Windows > Fonts folder and cut/paste all non-default fonts out to another folder so that you can check if this is in fact the issue. If Captivate then launches successfully, you start re-installing fonts until you find the one/s responsible for the crash.
