Local Admin workaround ?

I have been having this problem where we are in the process of removing all user from the local admin group. Everything has work great execept randomly I expericence some users not being able to start outlook but are able to launch word,excel,access with no problem. So I tried added the user as power users and that didn’t work so I had to put them back as a local admin in order for outlook to work. Anyone have any ideas or suggestions? Thanks for listening