You are trying to push a docker image to Nexus and Docker complains with a message similar to:
Error pushing to registry: Put /v2/ubuntu/blobs/uploads/
81ad3e90-544a-4bf6-88bf- acd92b479f69?digest=sha256% 3Aa3ed95caeb02ffe68cdd9fd84406 680ae93d633cb16422d00e8a7c2295 5b46d4: unsupported protocol scheme ""
This is a known issue that occurs when using Docker 1.7.1 (and probably earlier) with Nexus 3.
Upgrade to Docker 1.8.0 or later to solve this.