title: SourceTree filemerge quits immediately and creates 4 files. How to fix it?
body: <p>yesterday I could merge files in sourcetree with the external tool filemerge. Today, sourcetree wanted me to register me, and after my successful registration, I couldnt start filemerge. </p>
  
  <p>When I choose "Launch external diff tool" from the contextmenu of a file, 4 files appear (Backup, base, local and remote) but filemerge quits immediately.</p>
  
  <p>When I launch external diff, filemerge displays in the left /dev/null as source. How can I fix it? In preferences I choose filemerge as external diff tool. Have I to write the diff command for source tree manually, to give it the right local version of my file? How can I do it?</p>
  
  <p>Thanks</p>