Encountering QuickBooks error code 1638 indicates that you already have QBDT installed on your computer and are trying to install it again. You just need to locate your QB version and open it. This appears on the screen with a message saying: Another version of this product is already installed. To deal with this problem, we have given you a lot of information in this blog. Like if we talk about reasons, then a virus infection, wrong firewall set...