There has been a format change to the compiled output file.  As the
CHANGELOG says:

    Upgrading to v1.5 from any version prior to v1.5 requires an extra
    step for people who installed gitolite using the "system install /
    user setup" method described in doc/0-INSTALL.mkd.  For such
    installations, after the administrator has upgraded gitolite
    system-wide, each "gitolite host" user must run `gl-setup` once
    (without any arguments).

    This is *not* an issue if you installed using src/gl-easy-install.