Hello, I have the exact same issue with SIMS reports and letter definitions not opening either. It is an Windows 7 & RM Network with MS 2010 Suite but all settings have been altered for permissions should be fine. It seems to work if accessing the reports straight away after logging onto a workstation but it seems that the settings are still loading so the 2+ time of trying a 'Command failed' error is produced.
Any advice as these steps above haven't been successful.