Could you tell me if there is any difference in meaning between the following sentences?
When I got into the movie industry, I was waiting tables for seven years.
When I got into the movie industry, I had been waiting tables for seven years.
I would've thought that the first sentence isn't grammatically correct, but I hear native English speakers say it. I wander if both are perfectly natural and correct. If so, is there a nuance of meaning between them?