When the VLBA database was updated to a recent geodetic solution (2008a)
in Sept. 2008, an error was introduced for the GBT.  The trigger was a change
of name of the GBT from "GBT" to "GBT-VLBA" that was not noticed when the
new coordinates were loaded from the geodesy files to the VLBA database.  This
resulted in there being 2 entries for the GBT.  The axis offsets were not
updated at the same time so the new station got an offset of 0.0 meters
when it should have been about 8.9cm.  Correlator jobs created between then
and when the problem was caught in January 2009 had the incorrect axis offset.
During that same period, the VEX files created by SCHED also had a zero
axis offset, so if those positions were used for correlation elsewhere, the
same error would occur.

Note that the new GBT position and rates installed in September 2008 result in
a change in the position for the GBT used in correlation by about 3cm.  The
change is within the error estimates for the GBT position, which is not
nearly as well determined as those for the VLBA antennas.

Astronomic observers, particularly those doing parallax observations, should
consider whether these offsets are an issue for them.  If so, corrections
should be made.  Task CLCOR in AIPS is capable of making the necessary
corrections.