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The idea behind setting the minimum and maximum value of the
GUI Control NumericUpDown is that the GUI cannot have values
that are not supported by the domain.

Currently the maximum is always set to long.MaxValue. I
assume Adrian has changed that to ensure his model gets
generated without compilation errors. I cannot reproduce his
error.
For the future I suggest using the original implementation
that uses type.MaxValue where the type is the type of the
property because NumericUpDown controls are only used for
numbers and all built in number-types have a Min/MaxValue
property.