How to get data from serializer.DeserializeObject?

My data from a web service:

"[
    {\"RecordId\":\"7\",\"ReviewPeriod\":\"4/2013\"},
    {\"RecordId\":\"8\",\"ReviewPeriod\":\"1/2014\"},
    ...snip...
]"

And I am trying to parse it like so:

IdsJsonObj = serializer.DeserializeObject(ids_json) as List<Dictionary<string, string>>;

But when I then try to iterate over "IdsJsonObj" I get an error because it is null.

Anybody know what the heck I am doing wrong? :)

Thanks.
Eric