Please give more details what you mean by friend pat error then we can help =)
LAST night my friend tried petting my cats but couldn't thy showed error
What was the error message?
Often most errors or scripting problems can be fixed by putting the cat in and out of 3d to full prim mode, or to send it to the cattery and back into SL again. Perhaps try with other cats and see if it is the same issue, or just one cat affected. If it is just with one cat, you can always file a ticket to get a replacement for the cat if the other things I suggested do not work