Please offer some advice.

I'm afraid I have to disappoint you, but Excalibur simply cannot be a licensed game! It's an unofficial add-on for Heroes 4! Therefore, the disc is also unofficial, meaning it's a pirated copy. There are only two official add-ons for Heroes 4: The Coming of the Storm and Armageddon's Blade! There is one unofficial one - Equilibris, or rather, it's not an add-on, but a mod! What is Excalibur? It's a collection of fan-made maps and campaigns. They may not have undergone testing, or the testing may have been inadequate. So, no one is responsible for the quality of pirated products. I advise you to purchase a licensed copy of the original Heroes 4 from Ubisoft! And its add-ons. Or buy the Holiday Edition, which includes Heroes 1-4 with all the add-ons! It costs about 400 (or more) rubles, but a license is worth it. You can also download and install the Equilibris mod, as I've heard (I don't know for sure), it works perfectly even on pirated copies! This might help you. Just launch the game through it. However, I'm not sure if this will help... But you can try it. Sincerely, Luchik!