In the debug-logs of a user (C:\users\<username>\appdata\roaming\Watchful Software\RightsWATCH), the following line appears:
{0X80070002.EN_US}> Failed to init MSIPC!
ICT Mobile
User can classify information but cannot consume it / Reset AD RMS Client
If this didn't work there is another way to make it work with the old RMS Client (1.0) by setting a DWORD reg key (UseOldMailerEncryption) in the registry:
Under HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Watchful Software\RightsWATCH and HKEY_LOCAL_MACHINE\SOFTWARE\Watchful Software\RightsWATCH
Set "UseOldMailerEncryption" to 1.
3. If this still does not work, check that the integrated authentication is correctly configured to access the RMS
Open an IE as a mobile user, in the server, and try to access http[s]://[RMS_FQDN]/_wmcs/licensing/license.asmx (should not get credential prompt or any network related error)