Git Bash button doesn't work

After upgrading to 1.6.23, the button "Terminal" doesn't open git bash anymore, but ends in an error message of:

It has not been possible to start the Git Bash terminal.

My settings:

• v1.6.23 of SourceTree for Windows
• Checked Use Git Bash as default terminal (it works when just opening cmd.exe)
• I use System git. Previously 1.9.x, but now I upgraded to 2.6.3, still the same problem. I didn't try the embedded git.