Hi Lasse
I put your error message into the error decoder,
The rather interesting result is:
1. %RF_INTERDEV-4-RELOAD: % RF induced self-reload
The redundancy facility interdevice code is reloading this device because of a forced switchover or an error involving the dual active.
Recommended Action: If this message recurs, copy the message exactly as it appears on the console or in the system log. Research and attempt to resolve the issue using the tools and utilities provided at http://www.cisco.com/tac. With some messages, these tools and utilities will supply clarifying information. Search for resolved software issues using the Bug Toolkit at http://www.cisco.com/cgi-bin/Support/Bugtool/launch_bugtool.pl. If you still require assistance, open a case with the Technical Assistance Center via the Internet at http://www.cisco.com/cgi-bin/front.x/case_tools/caseOpen.pl, or contact your Cisco technical support representative and provide the representative with the information you have gathered. Attach the following information to your case in nonzipped, plain-text (.txt) format: the output of the show logging and show tech-support commands and your pertinent troubleshooting logs.
After all that I'd suspect an IOS Bug.