This depends on the fact that the install script (install_plugin.py) looks for "map.pm", but all plugins contain "Map.pm" under the APACHE directory.
Since it's case sensitive, the installation fails.
In my case I tried to install officepack: As a workaround I substituted all occurences of map.pm inside the python script (install_plugin.py) with Map.pm and renamed the following:
- Extension directory from officepack to Officepack
- officepack.conf to Officepack.conf inside [extension]/APACHE.
This way the installation concludes succesfully.