This usually means that the $dbprefix line in your include/config.php file is incorrect. Make sure that the line is commented or uncommented out depending on how you have it set up via MySQL or your hosting control panel.
For example, if you used "ss_" for your database but leave the line commented, it will lead the software to think your databases do NOT have prefixes and as such can't find the database you're defining.
Instead, make sure that line reads like the below:
$dbprefix = "ss_"; // Uncomment this line if this is a new install.
Adding the two slashes (//) in the beginning of that line "uncomments" the line.
If you're NOT using any prefix, that means you left the line commented during the initial installation. When you upgrade ensure that line retains its two slashes.