Problem with snmp

Please help me!
In nagios.log file I have this:
xec/nagios/check_snmp_if: “Use of uninitialized value in concatenation (.) or st
ring at (eval 1) line 154,”.
Maybe somebody know what problem with my nagios.
Thank a lot for your help.

Query “Use of uninitialized value in concatenation” on Google. It looks like this may be a Perl problem. can you check what version of perl you are running, the OS, nagios and nagios plugin versions.