SQL Server Admin 2014 :: Required Permissions To Enable Mirroring Session

I have a Windows NT group that is used to delegate certain database responsibilities to other members of staff and I am trying to grant permissions for the members of the group to be be able to establish database mirroring sessions, as in run the following:

ALTER DATABASE <database>
SET PARTNER = 'tcp://principal_server.domain.com:port';

Although the group has db_owner role membership to the user database which grants the ALTER permission on the database, the following is being generated in the error log when they get to this step on the intended Mirror instance after restoring the database correctly in preperation:

SqlDumpExceptionHandler: Process 59 generated fatal exception c0000005 EXCEPTION_ACCESS_VIOLATION. SQL Server is terminating this process.
* *******************************************************************************
*
* BEGIN STACK DUMP:
* 10/29/15 11:16:15 spid 59
*
*
* Exception Address = 00007FF9A6AF838C Module(sqlmin+000000000003838C)
* Exception Code = c0000005 EXCEPTION_ACCESS_VIOLATION
* Access Violation occurred reading address 00000000000000D8
* Input Buffer 210 bytes -
* alter database <redacted> set partner = '<redacted>';

As you can see, the statement is denied to the user. There are no issues with the database as I am able to run the same query successfully using my own sysadmin account after the failed attempt. What other minimum permissions the group might need to successfully enable them to setup a mirroring session?