Hi..
You should DEFINATELY UPGRADE to Combustion version 2.1.1 ! It is FREE...........
If you are already on Cv2.1.1, then tell us which codec you are trying to render to? It is hard to GUESS...
example: If it is a QuickTime MOV file, then re-install QT.
Lastly, whatever codec you use, WHERE are you rendering the file TO? It should be on a LOCAL DRIVE, and, that drive should have PLENTY of SPACE.. (duh.)
bye,
jack