Create ItemCard via Webservices through PHP

I am attempting to create a new ItemCard record in Dynamics NAV using PHP via webservices.

I am able to create an empty  ItemCard record without any issues. However when I attempt to "update" the newly created record immediately afterwards, I get the following error:

"Element "Key" in namespace "urn:microsoft-dynamics-schemas/page/itemcard" is missing from the message!".

The ItemCard object param looks like this:

ItemCard Object
(
    [Key] => 300;GwAAAACJBTcwMDk1AAAAA [ VERY LONG STRING ] AAAA=6;2311140;
    [No] => 70095
    [Description] => Hello World
    [Inventory] => 25
    [Gen_Prod_Posting_Group] => 
    [Unit_Price] => 1000 

)

 Anyone know what I could be doing wrong? Is the format of the Key wrong? What should it be? Any help appreciated.