Function Calling

Hi,
I created a function that fills a combobox with certain information.
The funcion is like this :

HTML Code: 

My function is working well.I just don't understand something.
When i call it like addCombAdm Combobox1 it works but when i call it like
addCombAdm(ComboBox1) i get the 424 error. What is the difference?

Thanks!

thank you!