Same issue on 8.0, but I was able to get to the bottom of it.
Ran the GUI with debugging enabled and saw this in one of the outputs:
[ 99] | Omniback::GetHostList: Could not read cell info file.
[ 99] | Omniback::GetHostList: Failed!
[ 99] | Omniback::GetHostList: Elapsed time: 0 seconds
[ 99] ------------------------------------------------------------------------
Doing a 'touch /etc/opt/omni/server/cell/cell_info' on the server addresses the "Object not found or access denied" issue, though then it was complaining about somethign along the lines of the GUI not being the right version to manage the CM even though they are both 8.01. I just added my CM as a client and installed disk and media agents and it updated the cell_info file. Everythign seems to be working fine now.
Perhaps the solution was to just add the CM as a client to begin with (i.e. skip the touch command)? Doesn't matter since it's working find now.
Thanks for your help,
Clay