In case you want to enable ECW Decode support, it is mandatory you agree with the ECW Eula. 
Moreover if you want to support ECW Decode in a Server application you need to BUY a license from ERDAS.

Note that with the latest GDAL 1.9.2 native libraries, the JP2ECW driver may crash on Linux 
using ImageIO-ext version 1.1.6. (The problem has been fixed on 1.1.7)
See ImageIO-Ext related ticket:
https://github.com/geosolutions-it/imageio-ext/issues/49

And the related GDAL ticket:
http://trac.osgeo.org/gdal/ticket/5024

You may skip that driver by defining an Environment variable (GDAL_SKIP)
GDAL_SKIP=JP2ECW