I was unable to commit csharp-files (*.cs). In the end the problem was that at some point i installed mod_mono, which made the *.cs-files inaccessible, through its configuration. So it may well be an apache-configuration issue, if only some sort of files are not accessible.
grep ".cs" /etc/apache2/mods-enabled/*
...
mod_mono_auto.conf:AddType application/x-asp-net .cs
...