error while assigning the driver to the shipment in dispatchboard or from action

I have planned the shipment and trying to assigning the driver to the planned shipment.but I am getting the below error while I am dragging the driver and trying to assign to the shipment from my login.

Read_Record_Failure(cachedUser=BTT.SIS/nul/ADMIN,Class glog.ejb.fleetassignment.ejb_DriverAssignment_ewcz 9g_impl,currentUserName=BTT.SIS,primaryContext=45, Vpduser=BTT.SIS/BTT.SIS/ADMIN)

same error it is throwing when I am assigning the driver from shipment action as well. Need some pointer why this error is coming?

Thanks,
Sirish