title: SourceTree external merge stopped working
body: <p>Ive been using tortoiseMerge as external tool in source tree for a while now but today I had 3 conflicts after pull, so I fixed the first one then I wanna open the next and window pops up saying Visual merge in progress, but nothing happens, tortoise is not launching. </p>
  
  <p>How could that happen?<br>
  It works one second and than it doesn't...</p>
  
  <p>I did some search but did not really find much, I tried to change diff tool in source tree from system default to tortoise, but that did nothing. </p>
  
  <p>Any ideas what happened?</p>