:It was an ID ten T 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?"
The computer guy 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 out ........ I D 1 0 T
I used to like Harold.