Comment 6 for bug 128617

please have a try with latest AMD/ATi drivers ver. 8.42. with those shipped with Ubuntu Gutsy 7.10 I experienced this problem too, but now after upgrading I can again suspend and hibernate without any issue.
http://www2.ati.com/drivers/linux/ati-driver-installer-8.42.3-x86.x86_64.run

please remember to run aticonfig --initial after installing and also that after each further kernel update you will need to re install them as far as the package will not be provided directly from ubuntu repositories.