The ARTARTNOT grid is based on the BKART file.  The check number which displays on the grid is a reference number.  The actual check number is in the MKECLASS file.  I would appreciate if the programmers would write a function field which would show us the actual check number instead of the reference number.  The reference number has no meaning to the customer.
 

I just loaded the Nov 2011 update.  The "Invc#" in the PAYMENT column is the actual invoice number.  I am looking for the customer check number that paid that particular invoice.  I ran SU-D grid maintenance and checked "replace".  Do we have different grids?

Lynn Pantic helped me with a the User Defined Function.  It works great!  If anyone is interested, the code is as follows:
 
//UDF6 will get the customer check number for the ARTARTNOT grid
func UDF6
   define mkeclass.h type I size 5
   if mkeclass.h = 0
     openv 'MKECLASS' fnum mkeclass.h lock N
   endif
   findv M fnum mkeclass.h key mkeclass.num val bkart.check
ret mkeclass.desc
 
Just follow the "User Defined Function" instructions on the ISTECH website.  Thank you Lynn!!