NLSPATH help!!!

What is the NLSPATH ???
I'm using my procmail since some months, but each time it filters a
message, it also shows an error:
     "## NLSPATH: Undefined variable"

What can I do ???
(there are no troubles, in his filtering... only that when I start my
 mailstat there are always these errors !!!)

Thanks in advance.
Filippo (from Italy)