If you promoted a member server to the MSS role (see “Promote a group member to Master Secret Server“), you might observe the BizTalk Administration console MMC hanging on startup.
Most comman cause is a setting in the General Tab in the BizTalk Group of the BizTalk Adminstration Console. The "Enterprise Single Sign-On server name" parameter is probably pointing to the old MSS server. Modify this to the new MSS name, restart the BizTalk group and the problem should go away.
MS also has instructions for “Changing the Master Secret Server“; agian, promoting a group server to the MSS.