I have a coworker that gets this error when he is using Raster 2011. In the <<Unnamed>> profile Raster initializes and works just fine. But when he has switched to another AutoCAD profile, Raster gets this error if Raster was not initialized previously. The workaround for this is he can just set <<unnamed>> current, start a Raster tool to initialize it, then switch back to his custom profile and it will work.
I'm wondering what else in his custom profile is set incorrectly so it cannot find the .dll necessary for Raster to work.