Hi shaunw,

1. Multiple files select issue.

The multiple files select function is based on html5/silverlight/flash plug-in of the browser, please ensure that his IE 8 has silverlight or flash plug-in install.

Let your client try on demo page http://aspuploader.com/demo/form-multiplefiles.asp, if this demo page works for you, then I suggest you download the latest build and try again. 

2. Got error.

In your client's pc, I think his firewall or antivirus prevent the upload, you can disable them to try again.

Regards,

Ken