GarageBand will not open since installing AKAI piano plug-in

I ma using GarageBand on a new 24" iMac. I signalled software for a midi controller, "Akai MPK mini". One of the plug-ins called mini grand that is provided with the midi controller did not install properly. More frustratingly, it is preventing GarageBand from opening. The error message is inserted below. I have uninstalled mini grand and used Clean My Mac X to run malware searches and make sure all remnants of the MPK mini are gone. Restarted the computer. Uninstalled and then reinstalled GarageBand. Nothing so far is working. Still the same pop-up. Can anyone help? Kind Regards, Andrew