I just debugged a problem that was manifesting itself as Hudson kept checking
out a fresh copy of the workspace even when there were no changes. The message was:

A SCM change trigger started this job
Checking out a fresh workspace because the workspace is not
https://SVNHOST.foo.com/rest/of/url

The problem ended up being that I specified the hostname in the job
configuration as all upper case (as shown), but the hostname recorded in the
.svn/entries file was all lower case - svnhost.foo.com. I accept full
responsibility for that buggering the job configuration, but the error message
wasn't as helpful as it could have been.

In IsUpdateableTask.invoke() in SubversionSCM.java, the code looks like:
if(!svnInfo.url.equals(url))

{ listener.getLogger().println("Checking out a fresh workspace because the workspace is not "+url); return false; }

I'd suggest changing the log message to something like:
println("Checking out a fresh workspace because the workspace URL (" +
svnInfo.url + ")is not "+url);

I'd be willing to submit a real patch for this if requested.