The .bls file saves bricks based on their datablock. However it will have an error where there is no datablock name where it expects one to be and stops mid-save.
8x Cube " -44 11 110 1 0 3 Letters/-space 0 0 1 1 1
+-ITEM HE-Grenade" 0 2 4000
8x Cube " -40 15 110 1 0 3 Letters/-space 0 0 1 1 1
8x Wedge" -40 11 110 3 0 3 Letters/-space 0 0 1 1 1
8x Cube " -36 15 110 1 0 3 Letters/-space 0 0 1 1 1
8x Cube " -32 15 110 1 0 3 Letters/-space 0 0 1 1 1
8x Cube " -32 15 106 1 0 6 Letters/-space 0 0 0 0 0
8x Cube " -36 15 106 1 0 6 Letters/-space 0 0 0 0 0
Spawn Point" -43.75 15.25 105.5 2 0 6 0 0 0 0 0
This is what a normal save file looks like, it has all the info on bricks in it. Your error will more than likely look like this:
8x Cube " -44 11 110 1 0 3 Letters/-space 0 0 1 1 1
+-ITEM HE-Grenade" 0 2 4000
8x Cube " -40 15 110 1 0 3 Letters/-space 0 0 1 1 1
8x Wedge" -40 11 110 3 0 3 Letters/-space 0 0 1 1 1
8x Cube " -36 15 110 1 0 3 Letters/-space 0 0 1 1 1
8x Cube " -32 15 110 1 0 3 Letters/-space 0 0 1 1 1
" -32 15 106 1 0 6 Letters/-space 0 0 0 0 0
8x Cube " -36 15 106 1 0 6 Letters/-space 0 0 0 0 0
Spawn Point" -43.75 15.25 105.5 2 0 6 0 0 0 0 0
It will load 5 bricks, come across the error of no datablock, then aboard the save. Your best bet is to go through the .bls and look for the error at hand, or give the .bls to someone who can fix it.