I have installed the shop, but met one problem based on an error in the manual.
When importing the ig_shop.sql dump the command should be:

mysql -uusername -ppassword yourdatabasename < ig_shop.sql

the manual instructs to use the mysqldump command, which will not work!

In my case the error described in the title of this message was created by the user-table, not existing...
Hope this is of help to anyone ;-)
Martijn