All you need is something like this(its extracted from a script I wrote for a workshop for kids):

Code:
function fish()
{
	while(1)
	{
		c_move(my, vector(key_w - key_s,key_a - key_d,0), vector(0,0,0), GLIDE|IGNORE_PASSABLE);
		wait(1);
	}
}


I can't see a wait(1); in your code.
If you actually didn't have any in your script, I wonder how it worked, anyway.

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt