Undo gignignore effects

We added a version information file to the .gitignore file to avoid stupid commits.
However, the file is still versionned and will be retrieved each time the checkback is checked out.
Now that we've gone to another iteration (from v4.5 to v4.6), I want to "ignore" the file, modify it and commit it, and finally reject it.

I tried
1) Remove the exclusion of .gitignore
2) 1) + Add Force Unignore rule in .gitignore (! Version.txt)

However, the file remains invisible throughout. I also checked my home directory and there is no global .gitignore file.

Thank you for your help