Welcome to this forum. I certainly hope that felllow list members will be able to assist with your problems.
Just a hint or two:
There are always extremely useful links under 'featured discussions' at the top of the page. These featured discussions are placed there when certain questions/problems pop up repeatedly. A handy link that's currently there: Important things to address when starting new threads!
A lot of problems are based on specific versions of NBU and version of O/S and advise given is then specific to the information supplied.

A bit more information of your setup will certainly help us to help you:
Is the Exchange server also the media server doing the backup?
Has this worked before or is this a new setup?
Does this have anything to do with your other post about removing a media server?

The error message that you are seeing seems to be master/media server comms related and not Exchange related.
So, as a start - we need info about your master and media server.