Are they both correct?
Usually, we disregard prepositional phrases when deciding number agreement between a subject and verb. The most obvious answer to your original question is (a): "There was a series ...". The subject is "series". The prepositional phrase "of meetings" is adjectival, describing the series.
Unfortunately, despite Bazza's harsh and ignorant reply, the question is not always that simple. There are a lot of exceptions.
Case in point: Going by what I said earlier, that last sentence should have been:
Here, "a lot of" is a set phrase that is interchangeable with the single word "many":
The subject is "people", not "lot".
Sometimes, collective nouns in the singular form can take either a singular or plural verb, depending on context:
The difference here is that in (4), the team is being described as a unit, whereas in (5), it refers to the individual members.
I would say that both of these are acceptable, technically, but neither sounds natural.
David, Gustavo, would you care to contribute?