Cargo publishing error: “failed to find lock source of …”

I'm trying to publish my package and get:

error: failed to verify package tarball

Caused by:
  failed to find lock source of mockers_codegen v0.5.2 (file:///Users/kriomant/Dropbox/Projects/mockers/mockers_codegen)

What does it mean?

Does running a cargo clean fix it? I'm not sure if that's a genuine error or just some ambient state thing.

cargo clean fixed it. Thanks.