Hi, we've had some small issues related to Express Scribe and lack of Admin rights on a workstation too - not quite the same as you, but related I think.
Do your users have full rights to the area that the dictation files are loaded??
We can load and play files from email attachments and local/network files, and users can change settings, we just can't do some things like "File" -> "Load Audio CD Tracks" - we just get a blank list where the tracks should be listed if they are not Administrators of the Workstation - so I think it's a rights issue over this device. Not sure though - only just realised that this was a problem today when someone wanted to do it.
Good luck fixing yours - I'm pretty sure it will be a rights issue on a directory or device.