I'm fairly sure only shields can parry. Internally, parry is just a shields defence value (shields also have a negative defence modifier but this comes from encumbrance).
manual p 77 (MISSILE COMBAT)
	Quote:
	
	
		| Attacker:  DRN  + (Size points in the square) +2 if magic weapon Defender:  2 + DRN + (shield parry value x2) – (Fatigue / 20)
 | 
	
 Not sure how accurate that is anymore.
There's a spell flag, "Misses do nothing" that might correspond to this:
http://wolfsbane.alwaysdata.net/Spells.html
I'd be interested to know the meaning of this flag for certain...  I'm guessing that it means the spell uses missile weapon rules.