Great Plains 7.5 Login Errors - Exception_Class_Form_Missing

have the great plains security options been changed for any users?

for example,  when security has been restricted for Human Resources, non-Human Resource users can receive this error when they log into the system.  

There are two resolutions if the human resources module is restricted:

First resolution is to give the user access the To-Do List and Personal To-Do List items.

The second resolution is to give the user access to the To-List and Personal To-Do List, then unmark these items in the User Preference window. Click Setup, click User Preferences, and then click HR button. Remove security again from the To-Do and To-Do Personal items.

check the security on users that cannot login - login in as sa and create a new user with all rights and test to see if this user can login