Have the two accounts point to the same library, preferably not located under C:\users but at a different path and be sure that the two users have RW rights to it.
Presumably account 1 is the one currently working correctly.
In account 1, open the library manager (file/library/library manager)
Select the correct library (presumably still Main Library ?) and click "Clone Library", specifying a correct sharable path and a new name (C:\JRLib for example, name it MySharedLib for example).
Switch to that new MySharedLib cloned library.
In Windows, give RW access to the new folder to account 2
In account 2, switch to that new MySharedLib shared library
Also, I had issues with MC server "keys" from client computers (or Gizmo), so I use IP_ADDRESS:52199 instead to register my server on clients. The MC server network key is not working if JRiver servers or your Internet are down...
And finally, beware of terms used. If you change a tag, it is changed in the library but depending of your settings, the tag change may not have been written to the media file. "Update Tags from Library" and "update Library from Tags" are your friends here...