Are you required to provide an original signature on a lien waiver?

Depending on what the contract says and whether the sigining meets e-signature requirements, yes, they can require a "wet" signature. Such a requirement would also protect you as well because a wet signature may be harder to forge than an electronic signature. Should this get to court, the copy that you scanned would be authenticated and binding, but I don't see the harm in providing the copy that you scanned and forwarded as the original to the GC.