i folled the install instruction to edit the php file and uniuploader. it seems to work great untill you try to add something to your shopping cart. i get an error

Warning: mysql_connect() [function.mysql-connect]: Access denied for user 'xxxxx'@'localhost' (using password: YES) in /home/kotgnet/public_html/roster/addons/shopping/functions_cart.php on line 33
Problem connecting

im not sure why or what to do.

Seems to me you did not enter the correct user credentials inside the functions_cart.php file.
Perhaps read the manual first!

That´s it

Type in the same things as for roster conf (DB, User, Pass...)
Save

and have fun