Every once in a while I get a transparent black screen scroll down over whatever I am doing with a message that says something along the lines of "Your macbook pro must be restarted, please hold the power button down until it turns off" there doesnt seem to be any rhyme or reason to it, it just happened while I quit safari. i couldnt find any info on why its doing this, does anyone have any answers? the computer is a 2.2GHz Core 2 Duo running 10.5.1 with 3 GB of RAM. thanks.