Before upgarding I upgraded all my widgets in Magento.
I updated with this: http://www.magentocommerce.com/wiki/1_-_installation_and_configuration/magento_1.5_to_1.6_upgrade and I got the error wich is mentioned in this forum several times (mysql 1052 and errno: 152 if I remember right).
After reading this: http://www.expertmagentodevelopers.com/blog/how-to-upgrade-from-magento-1-5-1-to-magento-1-6-0/
I also made the change in /app/etc/config.xml:
<initStatements>SET NAMES utf8</initStatements>
<initStatements>SET NAMES utf8; SET FOREIGN_KEY_CHECKS=0;
I changed the mage-file permissions to 775. After that I executed this command via ssh:
./mage mage-setup .
with the result:
(and something what already was in there and was not success because of that...)
Hope this helps: I´m not sure wich one of those the on who helped me? Mayby the mage-file permissions? and the xml? and the mage-setup? :D
And my Magento started working with multiple widgets in it.