You must enter a valid value for the Bargaining Unit field. - Error in worker load

Summary

Error in worker load for Bargaining unit field.

Content

Hello, 

I am getting an error in my worker load with an error message as "You must enter a valid value for the Bargaining Unit field". We have defined the value in the lookup for  "BARGAINING_UNIT_CODE"   but it still throw an error for all worker. I am able to successfully load the data with null value in the bargaining unit code column.  Any specific reason why i am getting this  error.

The values in the worker file for this column is same as iit is defined in the lookup.