vst instrument doesn't show up

I’m an inexperienced user of Cubase LE 5.
For whatever reason my Toontrack ezmix vstplugin doesn’t appear in the list unlike ezdrummer, which works fine. Both are installed properly and the respective dll-files are located correctly. The plugin path is also correct as other plugins from that folder can be selected.
Is there a limitation to how many plugins can be installed? I’m clueless. :confused: