Calypsochka, if you've already installed patch 1.3, then go ahead and install patches 1.4 and 1.5. In any case, you'll have to start the mission over from the campaign start menu.

I played this mission twice in versions 1.41 and 1.5. There were no glitches. But your phrase "the Necromancer never attacked (but of course, the army on the border is strong)" raised my suspicions. I didn't keep an army on the border, but tried to break through as many stat boosters as possible. First of all - magic and attack. I generally try to get the maximum possible out of each mission to make it easier for myself to complete the following missions. Maybe the game starts glitching because a hero with a strong army is located near the garrisons.