When you try to attach an attachment to a webutil fax you get an error and the following in the event log:

On the RightFax server I see the following error in the application event
Event code: 4011
Event message: An unhandled access exception has occurred.
Event time: 5/28/2014 8:00:12 PM
Event time (UTC): 5/28/2014 10:00:12 AM
Event ID: 21c7ffe9be6043d08b50b3c0a8be499f
Event sequence: 106
Event occurrence: 1
Event detail code: 0

Try the following:

1. On the IIS computer, browse to the ...\Program Files\RightFax\WebApps\WebUtil\Temporary Files\ folder.

2. Right-click the Temporary Files folder, and then click Sharing and Security.

3. On the Security tab, add Domain Users to Groups or Users, and enable the Modify permission in addition to the permissions already enabled for Domain Users.