Harold the Computer guy

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 it down...

I D 1 0 T

I used to like Harold.