Software :: Add More Files To Branch / Fatal: Unable To Write New Index File?

Dear all
I am new to git (and storing multiple copies of my code).

I was using git for one month (git status, git add, git commit) to store my files.

I have problems to add more files to my branch

git add BasisExpansion.R
fatal: Unable to write new index file

this was working great unless the day my system administrator destroyed my main partition (it was an accident) and installed everything from scratch. My home directory stayed intact (I did not lose any files not git files that are stored under /home). But from this point of time git returns always that error. My system administrator creater the same user and group as my old user was but this didnot fix the problem.

I am not sure If I can recover my old git structure or would it be better to wipe out the old git dir and start a new one?