The March 2021 security patches have given a lot to talk about. Although they apparently seemed like relatively small updates, installing them has triggered problems. A large number of users have found that when trying to print, Windows returned a blue screen with the code APC_INDEX_MISMATCH and forced a restart of the computer. And so over and over again. Printing was impossible. Now, a week later, it seems that Microsoft has taken this problem seriously and has finally released a fix.

The problems are related to the type 3 drivers of the printers. Currently, Windows 10 works with two types of drivers. On the one hand, there are the type 4 drivers, the most modern, which are included in Windows and reach users through Windows Update, and the older type 3 drivers that are not in Windows Update and must be downloaded. from the manufacturer’s website or install them from a CD or USB.

The blue screen APC_INDEX_MISMATCH that appears when trying to print is due to an error when taking control of the Type 3 printer driver. This error affects all printers with type 3 drivers (not a specific brand or model), so if our printer is relatively old we will be affected by the problem.

Temporary solutions to blue screen when printing

Yesterday we told you two possible solutions to these problems while Microsoft investigated the causes and solved it. The first of them, and the most obvious, was to uninstall the KB5000802 patch released on March 9 of this year. With this we expose our PC to the vulnerabilities solved with the latest patches, but at least we can print.

The second one is to execute the following two commands in a CMD window with Administrator permissions, replacing KX with the name of the printer driver:

With this, type 3 drivers should now work again in Windows 10 without launching the blue screen. However, if we want to do things right, now we can download and install an official Microsoft patch that definitely ends this problem.

Also Learn: How to fix error 0xc00000e9 in Windows 10

New update to fix printing problems

Just a few hours ago, Microsoft has released a new emergency update for Windows 10 in order to solve these blue screens when printing. This new update, already available on Windows Update, appears under the code KB5001567 (KB5001566 for Windows version 1909), and reaches users as an optional update.

All we have to do is click on the ” Download and install ” button that appears in Windows Update to download and install this new patch and put an end to the problems. As it is an optional update, it will not be installed automatically on our PC, but we will have to install it by hand.

We recommend that if we have no problems with our printer, we do not install it. These corrections will reach all users automatically together with the security patches of April 2021, so, sooner or later, our computer will be ready. But, if we do not use the computer to print, or our printer uses a type 4 driver and we have no problems, it is totally unnecessary.