Question

When in high school, my guidance counselor talked to me about career options. what kind of error does this sentence have?

Answer 1

It's actually a dangling modifier in this sentence.

Answer 2

I'd say that this sentence has a dangling or misplaced modifier.
The modifier when in highschool cannot be used that way, because we don't know for sure whether that refers to the guidance counselor or you. The correct way to write this sentence would be:
When I was in high school, ...