I don't think it's related to free or paid version.
When it happens to me, most of the time I've had the gimp opened and had worked for several hours.
C2 will close the project, and will "freeze" with no kind of message.
And if I go the task manager, then on display of the manager appears the default window message "C2 has stopped working".
No way to recreate it reliably though, also once windows applies some changes to the exe (?) it doesn't seem to fail again.
Win 7 pro 64 bits.
I still believe it's some unstability/uncompatibility between the QT library of Gimp and C2's GUI library.