What is ** Fatal: (vsim-8250) Class allocator method 'new' called on Abstract Class. about?

It means you called new on a virtual class. You must extend it and call new() on the extended class.

The there should be more messages that point to a line number. If it does not point to a line number, you may have to add this vsim switch ‘-voptargs=+acc=l’ and step through the code.