I experienced the same problem when I upgraded RP2.9 to RP3.11 - see the first post of this thread.
I'm doing this on a test site at the moment - I'd need to move it to a public site for you to be able to login.
Correct format: http://www.streetmap.co.uk/streetmap...180350&A=Y&Z=1
From RP extra field: http://www.streetmap.co.uk/streetmap...mp;A=Y&Z=1
The first URL is a 'good URL', the second URL is what RP is formatting the URL as when it's put into an extra field. If you click on the second link you'll see that it's not working.