Hi, I think this is a bug. When I define an Ext.grid.Panel with a store, and the store has a different value in the fields "userClassName and storeId" I got "Cannot call method 'on' of undefined" in Chrome, or "Item is undefined" on FireBug.
So, storeId and userClassName must be equal. Shouldn't this be addressed correctly in Designer?.
Thanks for reporting this. It appears to be a quirk of Ext4's MVC layer -- stores declared in the Application or in a Controller are registered in the store manager by their class name rather than their store id.
We definitely need to handle this in Designer in some way, whether that is always syncing storeId to the userClassName, switching components to use the userClassName in their store references, or some other solution. I will open a ticket for us to figure this out.
This is not a problem in Touch 2.0, by the way.
Sencha Architect Development Team