It is strange, I tried some things today.
1. On J 2.5 - when I uninstall all GK and K2, upgrade to j3.x works (Joomla installation is from quickstart 2.5)
2. When I install clean Joomla, upgrade from 2.5 to 3.x works
3. When I install clean Joomla install GK template and 3 modules (tabs, image, news) upgrade from 2.5 to j3.x works
4. When I install clean Joomla install GK template and 3 modules (tabs, image, news) and K2 upgrade from 2.5 to j3.x works sometimes
5.When I install J3 from quickstart there is few strange things.
- after clean quickstart installation articles here are not shown, please have a look at the screen
http://www.imagehosting.cz/?v=gknxn.gif- there is K2 2.6.7 after upgrade to 2.6.8, it writes this notification
Warning: set_time_limit() has been disabled for security reasons in /data/web/virtuals/xxx/www/subdom/demo/tmp/install_536380db33924/script.k2.php on line 119
- upgrade from J3.2.3 from J3.2.3 that is in quickstart to J3.3.0 works
It looks the error is somewhere only in J2.5.x in combination with K2 or GK or both. I have not found out anymore.