[AS2] Is there any documentation on how to communicate with flash using the invoke XML?

I'm trying to communicate with flash using Visual Basic. In my flash I have this:

ExternalInterface.addCallback("testFuncArray ", this, testFuncArray);

ExternalInterface.addCallback("testFuncString ", this, testFuncString );

function testFuncArray (_params) {

     fscommand('_array', _params.length);

}

function testFuncString (_param) {

     fscommand('_string', _param);

}

And in my Visual Basic I have this

xWin.CallFunction("<invoke name=""testFuncString"" returntype=""xml""><arguments><string>bleep</string></arguments></invoke>")

xWin.CallFunction("<invoke name=""testFuncArray"" returntype=""xml""><arguments><array><string>bleep</string></array></arguments></invoke>")

Invoking testFuncString works, but invoking testFuncArray causes an error, and I am 95% sure it is just because I have the XML for it wrong. I was wondering if anyone has any documentation for how this XML works?