If you are having problems with attachments in Service Portal, WebDesk or HelpDesk-Inernet Edition then the following can be one of the causes.
When files/attachments with different file extensions are attached or accessed in Service Portal or WebDesk you will get an error message if the particular file type or extension is not configured on the Web Server (IIS server) as a permissible file extension or file type. This applies also to HelpDesk Internet edition.
This can occur especially with newer file extensions like the office 2007 extensions (.docx, .xlsx etc.) which might not be added as permissible in IIS. This can also occur if the file doesn’t have any extension at all and the IIS Server is not configured to use wild card character mapping in the MIME type. Unlike previous versions IIS 6.0 doesn’t have wild card character mapping by default which means it will not serve files without any extension or with unknown extensions types.
This is also relevant if you want to restrict particular file types to the attachment feature in Service Desk or in Helpdesk (Internet edition). This can be achieved by taking out the particular file extensions in the MIME type on the IIS Server and do not use wild card character mapping.
Note: Allowing IIS Server to serve all files regardless of the type poses security risks.
Please contact your Web Server administrator to add or delete the particular file extension. If you would like more detail on how to set up MIME types in IIS please refer following tech notes from Microsoft:
For IIS 6.0
For IIS 7.0
Also please note that Service Desk allows attachments up to a maximum size of 4 MB.