Ensure you have cascaded ‘Full Control’ to every node in security.
Ensure you have saved this access within the security group.
Ensure the correct group has been selected for the security group.
Ensure the user in the Users form has the field ‘enabled’ ticked as he / she may not be enabled on your environment yet.
Alternvatively as it is ‘Full Control’ - simply add the user to Admin.
If you are still stuck I will e-mail you a full rights security group and you import this into your permissions which will overwrite all exisiting permissions for that group and resolve your issue.