I can't get into the elven mines...
 

I befriended the elves, destroyed the evil book in the elf land, finished the first prince fight, talked to Eric, talked to Rezo(and defended the tower for him, now he won't give me anything to do), and the elves still won't let me into the mines.
I'm not sure what I need to do.

Go the the other castle (bordered by mountains, had human armies before) in the same region and talk with this elven commander.

Are you talking about Kael Shot? I had all ready talked to him after completing the main quest of destroying the book. He thanked me and now has nothing new to say. The Iron Richard castle is empty. The King's castle appears empty after defeating the evil mage who was the king's ex wife.

NO, he mean the castle that usually used by iron richard, still in arlania

I went to that castle(before and after guarding Rezo's tower) and it says Iron Richard and his men have already left this place.

At this point you should zip a save and post it here so we can check it out ourselves.

I didn't realize I had to defeat the 4 undead armies to trigger the troops in Iron Richard's castle. Thanks for the help.