Cross Sell Advanced [Support Thread]

[DrByte]

That usually indicates a SQL error, and its details are in your /logs/ folder on the server.
This FAQ (which I find by using the Search and pasting in the error message) speaks directly to that issue: http://www.zen-cart.com/content.php?...-and-try-again

There's no error in any of my logs.

Perhaps. But "Warning: An error occurred, please refresh the page" always means a database error is occurring. So, somewhere you're missing a table, or using incorrect SQL syntax when making queries. The FAQ article gives additional ways of diagnosing.