Which contains a sentence error?
Myra loves dancing, and salsa dancing is now her favorite type.
Myra loves dancing, salsa dancing is now her favorite type.
Myra loves dancing; salsa dancing is now her favorite type.
Myra loves dancing. Salsa dancing is now her favorite type.
The error is in the second sentence. You need something to seperate your thoughts. The other answers use conjunctions, semicolons, and new sentences. The second sentence just uses a comma, which cannot work to separate the clauses. :D