I am having EXACTLY the same problem. I am running a G4 iMac with a 1.25Ghz processor and 1GB of RAM and thought that memory or processing power might be the problem.
In addition to the messages that you have popping up, I am also getting a message telling me that my chosen compression setting (ie HDV 1080 50i) is ‘not supported’ and that my computer is ‘out of memory’!?
I look forward to reading this thread as it develops.
Dan