I have gone through all previous correspondence and forum posts over the http:500 issue to identify a solution without luck.
I have checked the IIS logs and see that there is an ASP 0207:80004005 error when using the multiflash upload - I have 3.08 Pure Upload 3 installed. The http:500 error message appears within the Upload box but the files do get uploaded.
The issue I have is that I only get the http:500 ASP error when the user is uploading with Internet Explorer 7+. I have tried Firefox and Safari without issues on the same PC.