[Holub]

There is one place in X-Cart where this error can appeared - func.db.php

	foreach ($tbl as $t) {
		if (isset($sql_tbl[$t]))
			$t = $sql_tbl[$t];

		if (!isset($storage[$t])) {
			$storage[$t] = func_query_column("SHOW FIELDS FROM ".$t);
			if (empty($storage[$t]))
				func_header_location("error_message.php?access_denied&id=78");
		}

Seems like there are some kind of troubles with your database.