I have two tables training class and users, and a junction table user-class.  
I tried creating a combo box on my users form which would list the available
classes from the training class table, and upon selecting a class the
selected user will be placed in that class.  It did not work.

I selected columns CLASS ID, CLASS NAME, START DATE, END DATE,
EDUCATOR,TRAINING ROOM, all fields from the training class table.  I chose
Class ID as my unique ID.  when i select a value, I receive a message,
'cannot be edited bound to column class Id.'

What I am I doing wrong? Please help