"Flush Failed" when trying to defer a job

[oddball]

Hi. I have a friend who is trying to encode to DiVX5.01 for me but he is getting an error 'Flush Failed' or somesuch when he goes to save the AVI and ticks the box to defer the job.

VirtualDub 1.4c I think he is using. He is going to try a later build and see if that fixes it.

Any ideas why?