[otrs] Error after Update to RC1

Hello, I just updated from beta8 to RC1. Every thing seems to work well. I can open new tickets and an autoresponse is sent back to the sender. But if I try to answer the ticket, I get the following error: Can't use an undefined value as a HASH reference at /opt/otrs//Kernel/Output/HTML/Agent.pm line 1138. Any ideas? Thanks in advance Bye Ralph