Please help me to move some client from one SEPM to another SEPM with help of Management Server List (MSL)

Did you configure it?

Configuring a management server list

yes but it is not working

What are you seeing?

Did you set the SEPM that you want clients to go to as the first priority?

Are decommissioning one of the SEPMs? If you turn off the SEPM service on the old one, do they contact the new SEPM?

No,I want to move half the client from SEPM-A to SEPM-B

Create a new group in SEPM, break inheritance on it and move those clients in that group. Create and configure an MSL with the SEPM you want them pointed to as Priority 1 and assign to this group.

I had followed the same step, but i get an error  Disconnected from Symantec Endpoint Protection Manager (SEPM-B) on SEPM-A

On what screen? Provide a screenshot please.

Kindly find the snapshot

And I assume for the line above, it connected to the other SEPM?

Yes, and get disconnected

Are these two SEPMs part of the same site, replicating partners, or was SEPM_B created using SEPM_A's Recovery File?

If none of the above are true, then we're talking about entirely independent sites with neither knowledge of each other nor matching Management Server Certificates.  This means moving by MSL will not work, and you'll have change the sylink files on the clients you want talking to SEPM_B, to repoint them at SEPM_B.

For example:
http://www.symantec.com/docs/HOWTO81109

You can always use this simple method

How to deploy/update communication settings from your SEPM to your SEP clients machines with SEP 12.1 RU2 or newer

http://www.symantec.com/business/support/index?page=content&id=TECH199124