Hello guys. Got this error aswell since yesterday. Thought it was a matter of time and tried later to upload a map, but still the same. If someone have a solution I'll be gratefull 🙂
For more details this is what I've done:
I have canceled a map upload that have reached more than 100% and then tried again to finaly get the 6003 error.
Running 1.7.10 - Release (win 7)
Don't have the error anymore and I'm currently trying to upload a world. If someone fixed this issue then many thanks! If not I recommend waiting if you get this error and try later.