--- a/LetoDMS_Core-3.3.9/Core/inc.ClassDMS.php
+++ b/LetoDMS_Core-3.3.9/Core/inc.ClassDMS.php
@@ -1139,7 +1139,7 @@
 		if (is_object($this->getDocumentCategoryByName($name))) {
 			return false;
 		}
-		$queryStr = "INSERT INTO tblCategory (name) VALUES (".$this->db-qstr($name).")";
+		$queryStr = "INSERT INTO tblCategory (name) VALUES (".$this->db->qstr($name).")";
 		if (!$this->db->getResult($queryStr))
 			return false;