You do not have the required file permissions

We exchange project files over a shared git repo on remote server and somehow I just lost write access to some files:

Error cleaning build folder

You do not have the required file permissions

Storyboard three-way merge handling is PITA (might blog about it later) and then I can't even make a "really clean" to rebuild the project from scratch!

Naturally not repeatable right now, but got to figure it out in case if (WHEN) it returns. Here's some good looking pointers to StackOverflow:

• How to unlock xcode file to make edits from different computers?
• myProject is locked for editing and you may not be able to save your changes?
• Unable to unlock file for editing in Xcode 4?

Btw if you are not using a Time Machine, do yourself a HUGE favour: stop everything right now, get one 1TB external harddisk and start using Time Machine. Now! Really!! You will thank me :)