I found that you need to have a command line version of svn available on the path to make mhbuild happy. I used the one available here: http://www.sliksvn.com/en/download but there are others. If you do not have svn on your path…mhbuild blows up without a 'nice' error message.
I have just checked in a fix for this (revision 228). I will make a new release for mhmake later;