If you get something along the lines of -

fatal: unable to rename temporary pack file: Permission denied
Auto packing the repository for optimum performance.
error: failed to run repack
Pushing to ….

When making a push you may have a courrupt pack file within your git repo…

Using the shell you can rebuild the "pack" files by running -

git repack -a -f

Ok – so this didnt fix the problem….

Running git push from the command line gives much more detail than "Git Gui"…

will update this post when we get to the bottom of it…

Ok – problem is with 64bit version of Msysgit – the current beta is broken (1.7.0.2),  We have reverted to Git-1.6.5.1 which doesn't exhibit the problem!