Problem with surface becoming transparent in assembly. How can I stop it?

Hello,

In an assembly, some parts become transparent with no aparent explanation.

I try to revert it but none of the basic options fix this (change transparency, change material, view selection).

Has anyone had such a problem? How do I fix this?

I'm using solidworks 2008 SP 3.0.

Thanks

Joao

SolidworksAssemblies