BUG: Sim can't excavate

Problem
My sims can't excavate. They stomp and wave but don't do anything.

Cause
Unknown.

This bug has been around since the Ambition patch and it will affect any games that are at least patched to that level (you don't need Ambitions to have the bug).

Workarounds
None
Mod that solves the problem
Buzzler@MTS has made a HotFix Mod for this issue: Excavation Site Hotfix