DKs causing errors

I've had it a few times now and can't figure out whats happening.
Sometimes a dk just pounds me and nothing happenes.
Most of the time, I get an error the instant he does something.
Anybody know what causes this?

If its needed, I play a priest on Lordaeron and it happens guaranteed in Arenas.

I still have two errors open if I am wanted to post these.

ERROR #132 (0x85100084) Fatal Exception
Program: D:\. Downloads\Wrath of the Lich King 3.3.5a\Wow.exe
Exception: 0xC0000005 (ACCESS_VIOLATION) at 0023:0081D559

the error