Problem in executing background

Hi,

            I have developed a Z report in that while executing in foreground for limited period customer no is coming correctly(10 digits), while doing the same in background for unlimited period and while checking in spool or downloading to excel file the last 3 digits of customer no is missing. Even though the values are limited in background.

  WA_FIELDCAT-FIELDNAME = 'KUNNR'.  

  WA_FIELDCAT-REF_FIELDNAME = 'KUNNR'.       

  WA_FIELDCAT-OUTPUTLEN = 12.    

So please guide me how to rectify the problem.

Regards,

Watch point.