Computer Error

I was having trouble with my computer. So I called Harold, the computer guy, to come over. Harold clicked a couple of buttons and solved the problem. He gave me a bill for a minimum service call. As he was walking away, I called after him, "So, what was wrong?" He replied, "It was an ID ten T error." I didn't want to appear stupid, but nonetheless inquired, "An ID ten T error? What's that .. in case I need to fix it again?" Harold grinned.... "Haven't you ever heard of an ID ten T error before?" "No," I replied. "Write it down," he said, "and I think you'll figure it out." So I wrote down. I D 1 0 T .... IDIOT ....