I made a search about this problem and I found solutions that don't work for me as changing some values or modifying tableupdater.php. I did it but nothing changed. (http://forum.virtuemart.net)
May be those solutions were for different versions of VM, so, what can I do to increase the length of the description field?
Thank Guy!
Start with: http://forum.virtuemart.net/index.php?topic=79799.0