10.5.2 is not supported.   I've tried to make it work but it is only available in CUCM 11.5 onwards.

Multiline is supported on Cisco Unified Communications Manager release 11.5 SU3 and later. However, if you are using Cisco Unified Communications Manager release 11.5 SU3 and Cisco Unified Communications Manager release 12.0, you must manually instal...