Another PM is unable to open a master project by the general method of highlighting 2 projects in PWA Project Center and choosing to "open in Project Professional for editing". I am able to do so with no problem using the same projects.  We both have the same admin rights in Project Server. He does not receive any error, Pro just opens up an empty project.  The curious thing is that he can get this to work if he changes from auto-scheduled to manual task mode.  I actually read about someone else who stated the same thing (which doesn't make any sense to me) although I'm not being allowed to add a link to that previous article, which was on the office 2010-project forum under "unable-to-insert-a-subproject-into-master-project": 

Anyone have any ideas?  

Hi Naomi,

A first debug step should be to identify if it is related to the user profile or to the machine.

Try to log on another machine and if it works, this means that it is related to your machine. Then you could investigate IE settings like compatibility mode, trusted sites, emulation...

If it still doesn't work on another machine, it is related to your user profile. If you can do it (ie lost timesheets and any legacy related to your profile), you could delete it and recreate it.