SourceTree diff stopped working only for one specific repository

[Nouman Ahmad]

Hi guys,
I've been using source tree from last 1 year and yesterday suddenly my sourcetree diff checker stopped working. Attached below is screenshot of message from source tree:
I've tried following but none worked

1. Increase file size in options > Diff.
2. Changed file encoding form ANSI to UTF-8.
3. Reinstalled source tree
4. Deleted current repo and created new local repo

If any of you have faced this issue and have some solution please let me know

I'm using sourceTree version 3.1.3.3158