You had me going there for a minute :)

I believe the v2.7 and v2.6 in the error message refer to the binary storage format used by Storable, and not the actual Storable module version. The version of Storable on my dev machine is 2.15 (according to CPAN, 2.18 is now the latest). The version of Storable on my failed test machine is 2.13. The Storable changelog doesn't say anything about the binary format version changes (except for binary format v2.5 in version 2.0).

I don't think it's unreasonable to expect compatibility in a module between versions 2.13 and 2.15.

Indeed, other than bug fixes, there doesn't appear to be anything in the change log (or reported bugs) that would prevent basic Storable use (I'm storing simple hashes, nothing funky) from being fully compatible all the way back to version 2.0. What's a guy to trust if he can't trust core?