That error just means that you're running with use strict and have an undeclared variable.

perldiag:

    Global symbol "%s" requires explicit package name
    (F) You've said "use strict vars", which indicates
    that all variables must either be lexically scoped
    (using "my"), or explicitly qualified to say which
    package the global variable is in (using "::").
[download]

Odd that the explanation doesn't mention use vars, though...