You're experiencing a USB conflict.
While shut down, unplug the iMate - start up, and after startup is fully
completed, plug the iMate back in.
Chances are it will work properly now until the next time you have to
shut down or restart - then you will have to repeat this procedure.
This worked for me - may work for you:
In the Extensions folder - inside the System folder - find the iMate USB Driver
extension - click once on the name, then insert one space before the start of
the name. This will make the iMate extension jump to the head of the line
when you start up, so that it will be recognized before the USB software Apple
has built into the OS can take control.
Close all windows/quit all apps - shut down, wait a few seconds for the memory
to completely clear (leave the iMate plugged in). Now start up and see how it
works.
WDL