I have seen both versions in a slightly different context:

According to Snell's testimony the New York, New Haven and Hartford Railroad line in New York was profitable until it was acquired and converted to diesel trains
http://en.wikipedia.org/wiki/General_Motors_s...



Still, Nokia had been profitable until last year.
http://seekingalpha.com/article/626961-why-no...

So what is the right tense in the following example?

The business was profitable until 2010, when a competitor entered the market.

The business had been profitable until 2010, when a competitor entered the market.