As everyone knows, script custom actions are inherently evil. A security addition to Windows Installer 4.0 in Windows Vista means that script CAs are even more likely to fail; see Heath’s blog entry on the issue and Aaron’s follow-up.
But did you know that script CAs, evil that they are, nonetheless ship in Orca, MsiVal2, and even the WiX toolset? Shocking but true. The Internal Consistency Evaluators (ICEs) are implemented as custom actions in .cub files that are MSI databases with a vastly different schema you’re used to seeing. A couple of ICEs are written in VBScript so a misregistered VBScript engine will cause those ICEs to fail. As WiX v3 runs validation by default during linking (and on-demand using the Smoke tool), failed ICEs fail your setup build.
Of 98 ICEs in the version of Darice.cub in the Windows Vista SDK, only four are written in VBScript — yet that’s all it takes to fail your build.
If you run into the problem, check out the workaround Aaron offers before you take the drastic step of disabling validation.