Unable to process your request, click here to go back when editing users

Unable to process your request, click here to go back when editing users

HI, 

I have a problem with 2 of my users in zoho, I tried changing their profiles to admin but everytime I try this legend appears "unable to process your request, click here to go back", I tried with different users even with the ones recently created and I can make these changes.

Please help.