问题调用ASP.NET AJAX WebServiceProxy.invoke（）Javascript方法

I'm having a problem with some code I've written. I've had to anonymize it, but I can give the problem. This javascript runs inside an iframe, and is part of an object that gets instantiated. The problem in particular is that I get a repeating error every time that "Type 'Object' Cannot be converted to type 'Function'" in the invoke() call. However, in the IE8 developer addon, checking the typeof of the function I pass (this.AJAXCallback), it clearly says that it's a function being passed. Is there any particular reason this error might be occurring?I'm having a problem with some code I've writte