Hi walker1475,
Can you show me the full error message? It like that the message you posted only contains a part of it.
Does it happens with special file/size/extension?
Try set property "TempDirectory" to a location which your site has the write/read permission.
<CuteWebUI:UploadAttachments runat="server" ID="UploadAttachments1" TempDirectory="~/mytemp">
</CuteWebUI:UploadAttachments>
Regards,
Ken