It means you have likely installed something for Intel Macs that runs at startup that won't work with that Mac. If you moved a hard drive with Mac OS X 10.6 or later on it to the Powermac, that would cause such a problem. If you connected a hard drive with 10.6 or later on it on it that was running Target Disk Mode (booting the Intel machine holding the T key) to it, that would cause such a problem. If you attempted to install 10.4.4 or later system specific disc on a hard drive that was designed for an Intel Mac, and moved it to that machine, that would cause such a problem. If you attempted to install a GUID formatted partition hard drive as opposed to Apple partition map on the machine, that could cause such a problem.