Rebuilding IM & Presence Servers Failing

Now that IM & Presence servers are configured as subscribers in CUCM, rebuilding them isn't quite so straight forward. If you just try reinstalling them then you'll get a nice unhelpful error message like the below:

To avoid this, within CUCM you must first delete the Presence Redundancy Group that contains the IM & P servers, then delete the IM & P servers. You may also need to bulk update all End Users to disable "Enable User for Unified CM IM and Presence". Then you'll be able to successfully reinstall the IM & Presence servers without it failing.

Also watch out for bug CSCus27634, which affects certain versions of IM & Presence 10.5, it results in the Cisco Presence Engine refusing to start due to it crashing. If you look the traces for the Cisco Presence Engine you'll see something a bit like this:

*** glibc detected *** /usr/local/pe/bin/pe: free(): invalid next size
(fast): 0x0ada0010 *** ======= Backtrace: =========
/lib/libc.so.6(+0x70b91)[0x787bb91]