Looks like we can't reproduce the issue or there's a problem in the test case provided.
Using Grid Panel Generates Error
I have a very simple project with a Panel that is the initial view with a Grid Panel.
I don't change any settings on the Grid Panel and I get an error:
Uncaught TypeError: Cannot read property 'isStore' of undefined ext-all-debug.js:43765
When I do add a store I get:
Uncaught TypeError: Cannot call method 'on' of undefined ext-all-debug.js:13324
Can you attached the project here or send us an pm/email if the project has sensitive info.
Can you also add the steps to reproduce the error?
Sencha Designer Development Team
Here is a very small simple test app with the problem.
Okay using the project, how do we reproduce the problem?
It sounds like you are being affected by the Ext JS MVC issue that requires storeId and userClassName of your stores to be the same thing.
Making sure the storeId and userClassName were the same appeared to fix it.
I didn't know about that.
Thanks, we are going to make this more clear in future versions.
You shouldn't have to know about it.