Remote Desktop passes credentials but bombs out with displaying screen

Hi I am presently thousands of miles away from our Mailserver which means I cannot solve the issue in front of the machine. I use RDP to log in to check logs etc. All has been working 100% for years until I allowed Windows Update to run yesterday (which was a stupid move from overseas). Now when I try to remote in I get the correct username, I enter the password, it moves to the usual security certificate screen, I click on "Yes" it starts to establish the connection and then bombs out. Whether I run mstsc.exe with or without the /console switch same result. mstsc appears in the services on my local machine and then disappears. Both machines are win7 The only solution I see is to get someone to stand in front of the machine and carry out whatever instructions I give them to try to bring RDP back to life.

But what actions should I ask them to undertake?
Anyone have any ideas please?

I thought disabling mstsc, rebooting and then re-enabling...

I looked on the web and there are many hits but no-one seems to have a solution that worked.
At least I am not alone.

Thinking about it perhaps a recent Windows update makes a certificate mandatory. "The CA Root Certificate is not trusted.... blah blah blah... " I don't want to try "Install Certificate" before I hear from anyone.