This is a very common issue, and I completely understand why!
The issue here is because in line 81 of "change_const.m", the value of Constant is being set to 0, rather than '0'.
When you use setparam, the value for the constant block should actually be a character array containing a value, rather than an actual value! I know that's very unintuitive, but the solution is pretty straightforward from here.
To fix your issue, just replace line 81 with the following:
set_param('email_const/Constant','Value','0'); %note that the 0 should be enclosed in single quotes.
