Upgrading to 6.23 RC9 brings two RB1100AH in an endless boot loop. 
Yup, I experienced the same thing and reported it to MikroTik late on Friday (ticket #2014112966000035).
Appears to be a problem with the uniprocessor MPC85xx kernel. If I replace the kernel with the one from rc7, then the system boots and the rest of rc9 (kernel modules + userland) loads up just fine.
Have not yet tried the SMP kernel on the AHx2 yet to see if all Freescale PPC boards are broken, or just the single-core ones are. (rc9 will probably brick an RB800 the same way, for sure.)
Please note that “brick” here is a strong word. The damage is not irreversible. Just use Netinstall to downgrade to an older stable version of RouterOS, like 6.22, and your 1100AH will be back up and running.
– Nathan
Just in case.
Even RB850Gx2, I am sure that the Boot Loop has occurred at ROS6.23rc9.
Also contact the support for here I was.
Thank you very much for the reports. We are working on the problem right now.
The rc section on the download page is there for two reasons:
- for users to help us test changes (thank you for this)
- for users to check if fixes are working for specific issues reported, written in the change-log, or noted on the forum.
Please be careful not to use this version if you don’t have time to check that it works for you. These versions are ‘hot from the build server’ and the changes have not always gone through extensive test.
Yup, no worries, I fully understand the reason behind the rc series. I never test them on production equipment. I just don’t want 6.23 final to be released with this bug still there. 
– Nathan
Till now we are not able to bring the router up via netinstall. The 1100 finds the PXE Server, got an IP and resolves a mac but isn’t available in netinstall… - Maybe it is a problem with netinstall on that windows notebook. The router are 200km far away and they have to be send to check this disaster. - Before I’ve tested RC9 on two mips RBs without Problems
Thank you very much for your quick reports.
PPC issue is fixed at 6.22rc10,
http://www.mikrotik.com/download/share/all_files_6.23rc10.zip