I had this problem too. I was able to make adjustments and print the label. Check that both the buyers address and your return address is in the correct format. In my case when I checked the buyers shipping details their ebay username came up on the first line of the the address block. My address had my old postcode which wasn't compatible with my new suburb. 

Once these were both corrected the label printing was possible. It seems most of these label printing errors are to do with buyer and sender addresses.

Hope this saves some people their sanity : )