WinMerge returns "right path is invalid" error when launched from SourceTree

Question

I'm using SourceTree for Windows and I've set WinMerge as my external diff tool. When I click on the "External Diff" button WinMerge launches with the left path set to the appropriate file and the right path is empty. A message at the bottom of the WinMerge windows indicates "Right path is invalid!". I've tried using the custom option with combinations of $LOCAL, $REMOTE, and $BASE with each combination returning the same error. How do I get WinMerge to work with SourceTree?

asle9634 · Answer

I'm using it for GIT. I found a solution, I'll post it below.

asle9634 · Answer

Using Embedded Git fixed my issue. Go to Tools -> Options -> Git -> Click on "Use Embedded Git"

Ashley Wilson · Answer

I've been using WinMerge as diff tool without changing any settings, with a git repo. Are you using it for git, or mercurial?