Hi,
I'm using MVC and I've been having this same issue. Based on your last message, I downloaded the latest AjaxUploader.dll version 3.0 20101019 and I'm still having the same issue.
I noticed that even though it errors out on the file, the file did copy successfully to the Temp folder. However, this error comes up and then the file can't be copied because it doesn't come back in the action as one of the processed files.
How can I avoid this problem?
Thanks,
-Maria Nunez