Error: grid expression. Failed to execute (Weighted Overlay).

[LaurenCody]

I'm trying to overlay several rasters, and I keep getting this error message:

grid expression.
Failed to execute (Weighted Overlay).

I don't even know where to begin figuring out what this problem is! HELP!

[melaniewilliams]

If you are in Arc 10.0, you might want to install service pack 3.  It looks like there were several things it fixed for the weighted sum tool.