[otrs] RegExp Filter Error

Hello I get an error reported by cron when executing the filter. It seems that some content in mail does disturb it. The error is the following:

Betreff: Cron $HOME/bin/PostMasterMailbox.pl >> /dev/ null

^* matches null string many times in regex; marked by <-- HERE in m/ ^* <-- HERE @frentix.com$/ at /opt/otrs/Kernel/System/PostMaster/ Filter/MatchDBSource.pm line 75.

The incoming mail contains following part:

from user: bla ---2009-03-13 12:37:45,503 [TP-Processor7] ERROR OLATRuntimeException - OLAT::ERROR ^%^ E5 ^%^ org.olat.core.logging ^%^ bla ^%^ 78.34.71.37 ^%^ <URL> ^%^ Mozilla/5.0 (Windows; U; Windows NT 6.0; de; rv:1.9.0.5) Gecko/2008120122 Firefox/3.0.5 ^%^

What should I do in order to prevent the filter to fail or at least not to send this error reports? Thank you for your help. kind regards Roman