Hi Elakat,
That is strange... did you look at my table with the system variables in CP6, I describe the changes and the problems that occurred with the first versoin of 6.
http://blog.lilybiri.com/system-variables-in-captivate-6
This is only my intuition that makes me guess what happens in your case. Cp 5.5 had both variables rdInfoCurrentSlide (index starting with 0) and cpInfoCurrentSlide (index starting with 1).
The previous rdInfoCurrentSlide is no longer available in the list with variables. In the first release of Captivate 6 this caused problems in advanced actions, rdInfoCurrentSlide was automatically replaced by cpInfoCurrentSlide and that caused of course broken actions. This was normally patched in version 6.0.1, so that the actions were converted properly. And I think that this is the cause for your having twice the 'same' variable with a different definition. I don't have it in my list, but I never trust upgrading advanced actions, so mostly I delete them before upgrading. Especially in this conversion, because I was aware of the changes (as you will be suspecting, I was in the prerelease).
Widgets (external certainly) were broken as well.
This doesn't explain totally what happened for you, but could perhaps help. I would certainly clear the cache, eventually renew the Preferences folder and try again.
Lilybiri