Popup message requesting value - sql issues

Hi all,

I'm having trouble running this SQL. A message box pops up asking for the value of the string gbl_CommandPointer

Any ideas what i'm doing wrong?

DoCmd****nSQL "UPDATE tbl_PSA_Orders SET tbl_PSA_Orders.Sub_Category = (gbl_CommandPointer) WHERE (((tbl_PSA_Orders.Sub_Category) = (gbl_CommandPointer)) And ((tbl_PSA_Orders.fkeyPSA_ID) = [Forms]![Main_Sub_Items]![txtbox_SubItems_Ref_ID]))"

thanks
marcus