If you see permission errors when using SupportDesk (e.g. when adding attachments), then try adding the User IUSR_<YourIISServerName> (the Anonymous Internet Guest Account) with full access to the directories where SupportDesk is installed. This includes the directory where suppdesk.ini may reside and also where SupportDesk temporary files reside (in C:\supportdesk\Temp).
If the WebServer is installed on an NTFS partition make sure appropriate NTFS permissions are in place. Check the Properties of these directories (using the right mouse menu) and ensure that the User, IUSR_<YourIISServerName> has full access to both directories.