Calendar problem - fail to load view state

[Fernando A. Gómez F.]

Hello all.

I'm building a WebPart. In the CreateChildControls override, the webpart
creates a Calendar control in the following way:

_productCaducityDateCalendar = new Calendar();
_productCaducityDateCalendar.ID = "_productCaducityCalendar";
Controls.Add(_productCaducityDateCalendar);

However, when a postback is generated, it throws an exception with a
"fail to load viewstate" message.

I've been googling and this behaviour seems to happen whenever the
control's ID changes in a postback. However, the creation logic is
simple and I already ensured that the ID is the same.

Does anybody have an idea on what I'm doing wrong here? Any clue will be
really appreciated.

Best regards.