NSDictionary using contentsOfFile method doesn't build in Swift

I am building a dictionary using the contentsOfFile method, and pointing the method to a plist. My code is as follows:

func buildGraphicsDictionary() {

    var theme: String = "defaultTheme"

    var myDict: NSDictionary?

    if let path = NSBundle.mainBundle().pathForResource(theme, ofType: "plist") {
        println("path: \(path)")
        myDict = NSDictionary(contentsOfFile: path)
        println("dict count: \(myDict?.count)")
    } else {
        println("could not find plist file")
    }

}

The plist is found. I know this for certain because I am able to print out the path and because when I change the name of the plist string to one that doesn't exist I get an error. So I am confident the problem is not in accessing the plist.

However, when I attempt to print the number of elements in the dictionary using count, the console reports that the myDict has a value of nil. So this tells me that the problem is actually in the method by which I am building the dictionary (contentsOfFile). What is confusing is that I have seen other SO articles in which the same code is used (ostensibly) successfully.

Any ideas what could be going on here?