OK narrowed it down a little bit more.  The error is happening after the file uploads and before the fileuploaded event fires off.  I am now getting the error:  File: <filename> unknown result then it barfs up the first part of the html for the page then is cut off I presume by the messagebox size limit.

Somewhere about the same time this happens I am assuming is when the temp file is renamed from uploading..... to persisted..... as the temp file remains as uploading..... while whenever the upload is completely successful it is named persisted....

I have also had instances in the past when the file on the client computer remained locked and had to reboot my client to break the lock, although then the uploader was working properly.

 Now, since it is actually writing and creating files in the designated temp directory, the site obviously has read and write permission there.  The login used for the application thread is given full control on that directory so it should have full control on any of those files.  Is there some other directory that ajaxuploader uses that needs specific permissions?