The 1959 convertible cadillac is one of a kind, a famous actor drove it. which error is made in the above sentence?

The comma should be either a semi-colon or a period (a semi-colon would be better, imo.)

Think of it like this: the sentence "The 1959 convertible Cadillac is one of a kind" can be a full sentence on it's own. You could just period end and be done with it. ALSO, "A famous actor drove it." is a complete sentence on it's own, too.

Here's how to think of semi-colons v.s. commas:
Semi-Colons: Go in between two complete sentences (usually the two sentences are talking about the same thing, but both sentences can stand on their own as a lone sentence)
Commas: Go in between a complete sentence and an incomplete sentence, OR two incomplete sentences. (For example, in the sentence:
"I fell over, which made me embarrassed." the phrase "I fell over" is a complete sentence. You can put a period after it and it would make sense. BUT you need the comma because "which made me embarrassed" is NOT a complete sentence; that part doesn't make sense unless it's attached to an early part.

In Short: You need a semi-colon instead of a comma because commas connect incomplete sentences to other things, and semicolons connect complete sentences.