It has to be relative to your blitz basic program (exe or main bb file), not the text file. Maybe that's what you're doing wrong?
Edit :
Just try :
data/media/levels/articbase2.b3d
instead of :
../../data/media/levels/articbase2.b3d
Edit :
Just try :
data/media/levels/articbase2.b3d
instead of :
../../data/media/levels/articbase2.b3d