I'm a bit concerned to find that this thread was started in 2012, and meanwhile I am having virtually the same exact problem in 2015.
Regardless of what I seem to do in Project Manager I get the following (very infomative) error:
"An unknown error occurred during the Project Manager operation. Please save your project and retry the operation."
Now, I am using some 'long GOP' footage.
But has Adobe really not found a solution to that limitation in the past 3 years?
It would be good to see someone from Adobe comment on the limitations of the Project Manager.
Is there some place where the detailed limitations are spelled out?
Because right now my only course of action seems to be to toggle different options on and off and run my own tests in hopes of narrowing down the problem, because the only feedback the software gives me is "An unknown error occurred."