I recently had a customer with a problem where a user could see contacts in the Act database but couldn’t edit them. All of the fields were grayed out and made updating the address, name, etc impossible.
It’s an easy fix. On the computer that hosts the database, go to Tools > Manage users. In this list, find the user who is not able to edit entries. Edit their role to say “administrator” instead of “browse.” That should give them full control again.