I'll have a look at when I'm home, maybe there was something wrong with the creation of the MPEI-Package.
In the old MPI-Package there was a version field, where you could set a MP-Version, which is compatible with your plugin, but I can't remember to set that for the MPEI. STRANGE
I installed this plugin on two different MP 1.1.2 setups (one vanilla 1.1.2, the other upgraded 1.1.0 -> 1.1.1 -> 1.1.2) through MP Extension Installer. On the fist setup the plugin worked directly after installation. On the second setup, MediaPortal refused to start the plugin as described by earlier posts. Could the problem have something to do with whether MP was upgraded or not?
I noticed on the second setup that uninstalling the extension left MyVolume.dll in MP's plugins\process directory, even though MPEI no longer showed the plugin as installed. To my surprise the plugin could now be properly started in MP Configuration.
Scratch the last part: On another attempt starting the plugin failed again. Oh, well...