Cannot Insert, Update Or Delete ...

I'm trying to assign Optional Fields that I created in Common Services to to the A/R Optional Fields Module. Every time I press Save, I get this message: 

 Incorrect procedure. Cannot insert, update, or delete A/R Optional Fields until all other users have left Accounts Receivable and all other Accounts Receivable windows are closed 

When I look at the list of Users logged in,  nobody is logged in to any A/R module or screen at all and the only A/R Window that is open is the A/R Optional Fields Window which I need to have open to press save. Do I have to wait a certain amount of time?