launching knime in linux

I have downloaded and extracted http://download.knime.org/analytics-platform/linux/knime-full_2.12.1.linux.gtk.x86_64.tar.gz  (and also tried http://download.knime.org/analytics-platform/linux/knime_2.12.1.linux.gtk.x86.tar.gz).

Trying to launch knime always gives popup with:

"The Knime executable launcher was unable to locate its
companion shared library."

From command line :

  ./knime

I get:
"plugins/org.eclipse.equinox.launcher.gtk.linux.x86_64_1.1.100.v20110505: cannot open shared object file: No such file or directory"

(plus the popup)

I have an uptodate  Ubuntu 14.04.3 LTS 64-bit

There are two possible causes: either your system is not a 64bit system but only 32bit or you are missing GTK 2 libraries.