I just succeed in removing that error.
Try set your pear config to a different state.
pear config-set preferred_state stable
And then remove CodeSniffer with
pear uninstall php_codesniffer
And reinstall with
pear install --alldeps php_codesniffer
My preferred_state was set to 'alpha', but when I changed it to 'stable' the phpcs stated working again.