git rm --cached and fatal: pathspec

For the issue in the question title, you can generally solve it this way:

git rm --cached *

fatal: pathspec 'blah' did not match any files 

git ls-files

That will list the files git does have in its index, and you can then remove them explicitly one by one. If for example it lists img/blah.jpg:

git rm --cached img/blah.jpg

This will solve the pathspec error in the more general case, whether it's a branching issue as it was in the other answer here, or a new .gitignore entry, or a result of using 2 repos in the same dir, etc.

So, the solution is this:

The file is untracked in this current branch B

But it exists in the branch we are trying to check out, branch A, so we get a warning that the file in our current working tree will be overwritten (even though we aren't tracking it)

So:

1. delete the file in your existing directory (I just moved it somewhere out of the working tree initially to be safe) of branch B

2. check out the branch you want - i.e. branch A

3. Remove it from branch A using something like this:

   git rm --cached app.xcodeproj/project.xcworkspace/xcuserdata/u.xcuserdatad/UserInterfaceState.xcuserstate

Note: Fwiw, Branch A was my master branch. Branch B was my dev branch.