For example, if you accidentally type 3.0 or 2,500 (with a comma), it rejects the input and shows this message. I understand the integer constraint — after all, you can't have 2.5 copies — but the validator could interpret 3.0 as 3 without interrupting workflow. Also, the 1–20000 range is generous, but why not allow 0? Sometimes zero repetitions should simply mean “do nothing” instead of canceling the command.
If your hatch still won't generate, change the scale of your hatch pattern to a larger number in the Properties palette to reduce the line density. Fix 2: Increase the Array Bounds via MAXARRAY autocad please enter an integer from 1 to 20000