Lync 2010 - “sorry, but i can't seem to connect you to your conference right now. please try your call again, goodbye

Scenario
Multiple Lync Standard edition servers / 3 x Central Sites / each with Edge Servers, PSTN Gateways, (In this scenario we have  multiple Cisco Call Manager CUCM)

Symptom
Dial In conferencing, multiple pools / regions.
You may create a new conference in which Dial in numbers connect to other pools other than the one you created your conference on.

In this scenario if you dial the local Conference server / Mediation server that hosts the dial in number, all is well,  However if you dial in to the conference from another pool / mediation server. Then you may receive the below announcement.

“sorry, but i can't seem to connect you to your conference right now. please try your call again goodbye"

Further debugging on (AVmcu,CAAServer, CASServer,SIPStack) you may see entries in the logs like:
"cannot transfer the call to another pool"
or
"sip/2.0 488 not acceptable here"
or
"reject the incoming dial out from mcu"

Resolution
The problem is with the "enable refer support" option on the Lync Trunk Configuration, Untick this option on your Trunks, and all will be well.
MS Tests show that Refer does not work in the case of Lync-to-CUCM integration. Some call transfer scenarios do not work with Refer support. 
Basically, that’s all we need for Direct SIP integration with CUCM.

Full Details on how to configure Lync 2010 and Cisco Call manager can be found in this great document by: Danny Cheung & Taimoor Husain
Integrating Microsoft Lync Server 2010 and Cisco Unified Communications Manager
http://blogs.technet.com/b/nexthop/archive/2011/07/17/integrating-lync-server-2010-and-cisco-unified-communications-manager.aspx