Subject and verb must match in number.
I see this error all the time, and it's really getting out of hand.
The other day, I was watching some show on the Discovery Wings channel about some newfangled helicopter. The narrator -- who, embarrassingly, spoke with a refined British accent -- said, "The first of five prototypes are scheduled to fly next year..."
(If you don't understand why that's an error, please email me.)
Number (Score:2)
Semantics (Score:1)