Problem: The latest version of Xquartz (2.7.5+) does not work with Tecplot.
Solution: Download Xquartz version 2.7.4 here: https://xquartz.macosforge.org/trac/wiki/X112.7.4
Yosemite (Mac OS X 10.10) Users
Tecplot will not launch on Mac OS 10.10. A Tecplot update is expected from the vendor by the end of December, 2014.