You must have some pack and unpack subs defined in the current package... Yes it works as it should, as CORE::pack() and CORE::unpack() are used, just like the warnings say.

So what can you do? Like the warning says, use CORE::pack(...) or &pack(...) in your call, instead of plain pack(...), making clear which one you want, or just don't use "pack" as your sub name. Ditto for "unpack".