InfoPath Dev

Hi I'm using the code below to call a function which writes a value to a field on my form. http://blogs.msdn.com/infopath/archive/2005/06/17/430347.aspx

I'm calling the function from a rule and it works perfectly if I use the code exactly as above. If I change the code so that instead of popping up a message it writes the param to a field I get the error below:

msxml5.dll

Attempt to modify a read-only node.

Error occurred during a call to property or method 'Test'.

 

Can anyone help me with this?

It would appear to me that the field is set read-only and not allowing input.  I would verify that in the view where you are trying to accomplish this that you can manually edit the field.