Edit: my bad, I DID have another mod installed. Apparently this conflicts with Optimine somehow, which is a very big issue. Any chance of compatibility? Also - would it be possible to make the hidden blocks only partially transparent? It's presently impossible to discern between invisible stone and air, which makes falling into caves a possibility. This would also make tunneling easier, as you currently can't tell except by sound what kind of block you're wailing on.
I'm running x-ray (version7 - non-modloader version) along side optimine (as well as zombe's mods, SMP shape builder & TMI) and I don't have any problems. Perhaps there's another mod you have installed that's conflicting? Whenever I have problems, I start with a freshly downloaded minecraft.jar and install just the mods that I think would be conflicting and then watch the java console - I run java -jar Minecraft.jar (the launcher) so I can view the output on the command line.
how are you using the shape builder... Its not updated.
It's under active development by a different group. Zaneris had give the source code to one of the other developers and now there's a few of them working on it. Do a search for SMP shape builder.
Could you create a version of this mod that makes everything bright. just like this mod, but without the xray part. it could even be the same mod but mapped to another key: x=xray and c=superbright?