How to solve virtuemart router problems

Hello experts!!!!!!
I need help to solve virtuemart router.php problems. I have just upgraded a Virtuemart installation to VM 2.0.12. The problem is that after upgrading I have been getting a problem like this:
Notice: Undefined index: categories in /home/proequip/public_html/components/com_virtuemart/router.php on line 2059
I just don’t know what should I do? Can anybody help? Thanks in advance.
