MissingMethodException in SmartPhone

[okaminer]

I've created a new application that contains 2 projects
A SmartPhone project and a Class library project. I'm still on the
Emulator

I've created few classes in the Class library project and then tried to
create instances of those classes in the Phone Project

The problem is that I can create the class but when I call one of it's
functions I get "MissingMethodException", which is weird because I know
the function is there

Is it wrong to use Class library project in SmartPhone application?
Should I stick to one project?

Can any one tell me what the problem might be

One last remark, The classes I've create are inherited from base class,
I hardly think that is the problem but than, hay, you can never know

thanks

 

[okaminer]

I've found the problem
I was using XML Document object in the Library class and in it I used
the function SelectSingleNode which doesn't exists in the SmartPhone
Framework
So when I got to the function that inside was the SelectSingleNode
function the program crashed

Still I would like to know if there is anything wrong with using more
than one project?