Я маю болить горло is not accepted - can somebody tell me why?
You cannot substitute "Я маю" for "У мене" in this case. It is like saying "I have a the throat hurts."
You can say "Я маю хворе горло" (I have an ill throat), but it is more like having a more serious disease.
Why would "У мене є болить горло" be wrong in this case?
A noun must follow after 'є'. And since 'болить' is a verb, you can't write 'є'