Not a good idea
Please do not remove any standard modules via the setup! If you do not want to see modules in EGroupware or do not want to make them available to users, then take away their execution rights.
You actually only need these functions to install or remove further/own modules.
You probably no longer have execution rights.
Have a look in the setup:
There you can create a user with admin rights or give full admin rights back to an existing user (who previously had them(?)).
Please try this out (after a backup!!!).
I have never had to do this before, so I am not entirely sure.