i got round this by changing the dependancies rather than injecting the meta (as injecting the meta makes the size of the map bigger and it cannot handle a change in size) hope this helps!
I guess your modding halo 2 so i suggest the following steps
1> Open Dothalo
2> Select The Map
3>Select lets say the weap tag for Magnum
4>Click on the Dependancy Window
5>Goto Proj dependancy and switch the dependancy in the scroll box above it and select say Beam Projectile
5> Save Changes
6> RE SIGN
7>NOW THE MAGNUM SHOOTS BEAM RIFLE SHOTS
And Your Done
ZENON
Think its time i oiled the rusty joints and see if i still got it