If you have a pit of fire or lava, is there any reason to not allow the barrier power to be used to create a bridge over it?
This is a general question having to do more with your play style, the same question has been posed over time with D&D Wall spells.
Do you want your mode of play to be legalistic? Are you concerned about "game balance" above all? If you "let" your players do this, then will you have a problem saying no when they take this justification and abuse it to try to make stairs, make a wall inside a dragon's stomach, etc? If so, you would tend to adhere strictly to the rules as written, and say "No! This makes walls and that's it!"
Do you want your play to be open-ended and you are comfortable with exerting GM control? Do you want to reward innovation and non-combat activities? Then of course you can allow it. It'll even be entertaining since the bridge will be VERY narrow and a Toughness 10 hit will cause the whole thing to crumble to dust.
Are you a game world realism fanatic? Then you probably will allow this, although not let it go for more than a short span without having bolsters from underneath (which maybe they could also build with Barrier but not over lava or water really) and you'd let them additionally use it for whatever the laws of physics dictate that they could. Here, you have to think hard about the ramifications of allowing Wall to be the "ultimate building block" spell because you will be reluctant to GM fiat out uses that still seem to fit the same game world physics model. In that case I'd allow it for short spans but not let them iteratively "build onto" it with additional spells to make complex structures.
I would tend to say that the default Savage World culture would fall into camp #2. Different games have different driving concepts - 4e would fall strongly into camp #1, a lot of indie games and early D&D into #2, and a lot of big trad games like GURPS or 3e into #3. Savage Worlds is one of those more crossover ones, though, where some people play it with a variety of agendas.
What I did:
I allowed it. I think I said the caster needed a Raise. I did a non Ace'ing damage roll from the lava against the Barrier each time some one walked over it, as it flex and go closer to the magma pool. If it did more that the max damage of the Barrier spell (10 IIRC) then the Barrier failed. Which did happen to the last PC, I then allowed a Jump test to see if they could make it across the last bit before the Barrier melted away.
Thanks to Dr Rotwang and mxyzplk for their answers.
I think on further reflection from the other answers and the events of the game. I would now rule the same, with some way that the weight of the characters might break it as it is thin (but you can climb it). Also I don't like the spell being expanded past this usage. Stairs no, ramps yes. Large diameter curves on a single Raise (but no power reduction), but no small curves to create a shield inside a dragon stomach.
I'd allow it. It's clever, it overcomes the obstacle and it moves the game along. Certainly there might be a few drawbacks, like mxyplk pointed out. Most importantly, however, the PCs get to win that one through clever use of what they've got.
And aren't we all at the table to have a good time and be awesome for a while...?