SB v5.31.4 "The Windows Installer Service Could Not Be Accessed" when trying to install programs.

This is still not fixed, sigh.

Many programs that have been installed in sandboxes just before those critical updates in Win10 when particular sensitive things were broken with Sandboxie or even under previous versions of Windows (7, 8, 8.1) still continue functioning flawlessly with any current Win 10 build. But we cannot deploy them afresh within a sandbox anymore. Some users here or in other forums suggested installing such programs on another machine (e.g. virtual one) running Win 7 or Win 8.1  then moving sandboxes back to the actual host system. The next problem is that  specific applications are strictly hardware-dependent, that is why they totally fail to run with hardware changed. And even a VM may be  technically perceived by them   as a different hardware configuration. I personally  use a Win 8.1 instance (the most modern, MS supported but still compatible version) with Sandboxie installed on an virtual drive (VHD(X)) either. But I have added it to the main boot menu of my PC instead of  letting it boot on a virtual machine (there is a lot of information on the internet  on how to do that). Not imperative for each and every application though. This is only to make the hardware set-up recognized by the application 100% identical. Besides that, the installation process runs faster and  more predictable on a real machine than on a virtual one. The bad side is that  two successive physical reboots are needed every time when trying to install anything in that way.

So, the whole installation procedure shall be as follows then:

Reboot. Chose the relevant Win 8.1. boot menu item. Install yor desired application sandboxed. Reboot again. Attach your VHD(x) (this is necessary when you have placed  the Sandbox folder on the System disk  under the Win 8.1). Find and move the sandbox containing the installation to the Sandbox folder of your  host system. Attach it to your sandbox list  ( by creating a new sandbox entry named appropriately or by giving the sandbox the name of an already listed one). Run your application sandboxed under the current Win 10 build.

This might be the only reliable workaround to date.  Unluckily.

Many programs that have been installed in sandboxes just before those critical updates in Win10 when particular sensitive things were broken with Sandboxie or even under previous versions of Windows (7, 8, 8.1) still continue functioning flawlessly with any current Win 10 build. But we cannot deploy them afresh within a sandbox anymore. Some users here or in other forums suggested installing such programs on another machine (e.g. virtual one) running Win 7 or Win 8.1  then moving sandboxes back to the actual host system. The next problem is that  specific applications are strictly hardware-dependent, that is why they totally fail to run with hardware changed. And even a VM may be  technically perceived by them   as a different hardware configuration. I personally  use a Win 8.1 instance (the most modern, MS supported but still compatible version) with Sandboxie installed on an virtual drive (VHD(X)) either. But I have added it to the main boot menu of my PC instead of  letting it boot on a virtual machine (there is a lot of information on the internet  on how to do that). Not imperative for each and every application though. This is only to make the hardware set-up recognized by the application 100% identical. Besides that, the installation process runs faster and  more predictable on a real machine than on a virtual one. The bad side is that  two successive physical reboots are needed every time when trying to install anything in that way.

So, the whole installation procedure shall be as follows then:

Reboot. Chose the relevant Win 8.1. boot menu item. Install yor desired application sandboxed. Reboot again. Attach your VHD(x) (this is necessary when you have placed  the Sandbox folder on the System disk  under the Win 8.1). Find and move the sandbox containing the installation to the Sandbox folder of your  host system. Attach it to your sandbox list  ( by creating a new sandbox entry named appropriately or by giving the sandbox the name of an already listed one). Run your application sandboxed under the current Win 10 build.

This might be the only reliable workaround to date.  Unluckily.