Dear twnewbie,

The employment discrepency, was it a negative termination (would the employer say bad things which surrounded your final exit from employment)?  

If it was a negative experience, it is mandatory that your clear things up as soon as possible.  It has already been looked upon as a negative since  "some phone calls you have received during the background investigation last week."  The agencies are paranoid about their appearance and such ommission is going to immediately raise flags about the rest of your application.

Take care of business immediately.

Regards.