Perl script doen't work for a specific user

[Patrick Nelson]

FC1

I set up a script that calls sa-learn (from spamassassin)  on one FC1
system this works just fine but on another system is errors.  Here is
the basic call:

su filter -c "sa-learn --spam <mailbox>"

The systems are identical except for something that fails on the one
system.  If I log into the system as filter like:

su -l filter

and then try and just run sa-learn I get a bunch of errors like:

Can't locate Mail/SpamAssassin/CmdLearn.pm in @INC (@INC contains:
/usr/lib/perl5/vendor_perl/5.8.1/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.1
/usr/lib/perl5/5.8.3/i386-linux-thread-multi /usr/lib/perl5/5.8.3
/usr/lib/perl5/site_perl/5.8.3/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.2/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.1/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.0/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.3 /usr/lib/perl5/site_perl/5.8.2
/usr/lib/perl5/site_perl/5.8.1 /usr/lib/perl5/site_perl/5.8.0
/usr/lib/perl5/site_perl
/usr/lib/perl5/vendor_perl/5.8.3/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.2/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.0/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.3 /usr/lib/perl5/vendor_perl/5.8.2
/usr/lib/perl5/vendor_perl/5.8.0 /usr/lib/perl5/vendor_perl) at
/usr/bin/sa-learn line 46.

This seems to be so for all users but root.  What would be controlling
this?  Any ideas would help...