If you find that Pitt Ohio Ground is unable to ship, check the logs to see if the Ship Response shows an "<Error>Not authorized</Error>" message. If so, then check to see if there are open packages.
From Pitt Ohio Ground (in this instance, at least) it showed that there was an OPENTRANS and then a CLOSETRANS that were produced in their system almost immediately. If this is the case, then do an EOD close... this should resolve.