He sent this to me separately, but the contents are as follows:
deny from all
I've not seen WP do something like this. If it is in the plugins folder you should be denied access to all plugins that are happening via http.
I do have 2 files with these rules that I included in the plugin. They appear in 'libraries' and 'scripts'. But should not ever appear in the main plugins directory.
Ovidiu, if you are getting this it is from somewhere else, and you can be sure that that is causing the 403 errors that you have. As for WP-phpMyAdmin, are you sure that you uploaded the entire directory, as it comes when you unzip it, to your plugins directory? However unless the .htaccess thing is fixed, the plugin won't work. Try deleting the htaccess file for now and test the plugin so that you can close this thread and start a new one to address the htaccess problem specifically.