Initialise repository for Git Flow failed in sourceTree

I got below error when I tried to initialize repository for Git Flow. I did switch Git by using embedded Git and System Git but still got the same error. Please advise.

sh.exe C:\Users\userName\AppData\Local\Atlassian\SourceTree\gitflow_local\gitflow\git-flow init -d
0 [main] sh 11680 fork: child -1 - CreateProcessW failed for 'C:\Users\userName\AppData\Local\Programs\Git\usr\bin\sh.exe', errno 13
C:\Users\userName\AppData\Local\Atlassian\SourceTree\gitflow_local\gitflow\git-flow: fork: Permission denied
C:\Users\userName\AppData\Local\Atlassian\SourceTree\gitflow_local\gitflow\git-flow: line 73: /gitflow-common: No such file or directory
Completed with errors, see above.