Failed first attempt when inviting friends using the Prime31 iOS Facebook Plugin

Question

I'm trying to open an invite box using the Prime31 Social Networking plugin. The problem is the dialog will always fail to load first time. After the first fail, the dialog box will work from then on. Restart the app, and it fails first time again. I'm opening the dialog box using the following code.

var options = new Dictionary<string, string>();
options["message"] = message;
FacebookAccess.showDialog("apprequests", options);

When I try this, this is what I get in the error log

2012-05-14 17:47:30.790 heroescall[158:707] error description: Error Domain=NSURLErrorDomain Code=-999 "The operation couldn’t be completed. (NSURLErrorDomain error -999.)" UserInfo=0xec7c890 {NSErrorFailingURLKey=https://m.facebook.com/dialog/apprequests?access_token=[TOKEN]&message=I%27ve%20answered%20the%20call%2C%20will%20you%3F%20Play%20Heroes%20Call%20for%20free%21&exclude_ids=&app_id=YYYY&api_key=YYYY&redirect_uri=fbconnect%3A%2F%2Fsuccess&sdk=2&display=touch, NSErrorFailingURLStringKey=https://m.facebook.com/dialog/apprequests?access_token=[TOKEN]&message=I%27ve%20answered%20the%20call%2C%20will%20you%3F%20Play%20Heroes%20Call%20for%20free%21&exclude_ids=&app_id=YYYY&api_key=YYYY&redirect_uri=fbconnect%3A%2F%2Fsuccess&sdk=2&display=touch}
2012-05-14 17:47:30.793 heroescall[158:707] error userInfo: {
    NSErrorFailingURLKey = "https://m.facebook.com/dialog/apprequests?access_token=[TOKEN]&message=I%27ve%20answered%20the%20call%2C%20will%20you%3F%20Play%20Heroes%20Call%20for%20free%21&exclude_ids=&app_id=YYYY&api_key=YYYY&redirect_uri=fbconnect%3A%2F%2Fsuccess&sdk=2&display=touch";
    NSErrorFailingURLStringKey = "https://m.facebook.com/dialog/apprequests?access_token=[TOKEN]&message=I%27ve%20answered%20the%20call%2C%20will%20you%3F%20Play%20Heroes%20Call%20for%20free%21&exclude_ids=&app_id=YYYY&api_key=YYYY&redirect_uri=fbconnect%3A%2F%2Fsuccess&sdk=2&display=touch";
}
14/05/12 05:47:30.860 (4.029738s) - Facebook Dialog failed - The operation couldn’t be completed. (NSURLErrorDomain error -999.)

Any suggestions? It looks like it's something happening underneath Prime31, in the FB library, but I'm not sure exactly what.