Today I created a new Mercurial repository on a Windows server.  I cloned it, made some changes, tried to push, and was greeted with this:

C:\myapplication>hg push
pushing to http://servername/myapplication
searching for changes
abort: HTTP Error 500: .hg\store0changelog.i: Access is denied

My user account had write permission to the myapplication folder on the server, and the odd thing is that I’ve created repositories there before and never had a problem pushing changes.  I compared 00changelog.i to the same file in another repository that was working.  Turns out I was using anonymous authentication and IUSR was missing write permission.  I gave full control to IUSR on hg\store folder and…

C:\myapplication>hg push
pushing to http://servername/myapplication
searching for changes
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 1 changesets with 114 changes to 114 files

Success!

If you’re having problems pushing to a central server with Mercurial, make sure the IIS anonymous authentication account (IUSR or IUSR_MachineName) you have write permission to the hg\store folder and subfolders in your repository.