Trying to install Document Seller. First attempt to install I got an error telling me I needed to enable the System - Legacy plug-in. Afterwards, I get an error "Plugin Install: No plugin file specified". The ZIP file contains "en-GB.os_authnetsim.ini", "os_authnetsim.php" and "os_authnetsim.xml".
Joomla version is 1.5.23
Any ideas?