Could not find UpdatePanel Error

I'm not sure why you are getting the error, but one thing I do know is that the CountrySelector contains an update panel around the States dropdown and hence you may be getting the the error because of this.

A workaround would be to change the CountrySelector to simple drop down lists. You would need to specify the Has depending fields accordingly and you can set the visibility of the state control by checking the content of the Country field.

I figured out that if you use macros to handle a webpartzone's visibility, regardless of if it is visible or not, the form is still loaded on the page even if it doesn't show in the code. My solution was to add conditional layouts around the webpartzones and added the visibility logic there. I could be wrong, but I think that because the page layout loads before the zones fully load, adding the macro to the zones instead of the page layout causes them (and their web parts) to still be loaded and processed.