Quick installer fix for GDAL 1.6.0. It installed support files in the GDAL 1.5 folder. You should also reinstall 1.5.3 to make sure the correct support files are present for 1.5.
“The beast is actively interested only in now, and, as it is always now and always shall be, there is an eternity of time for the accomplishment of objects.” – the wisdom of Tarzan