[Simple]

If you are getting "psaAagent.exe" error or missing DiagBox tabs on VirtualBox, then entering a System Serial for the Virtual Machine (as described below) and installing VC++ 2008 resolves it.

- Start an Administrator's CMD and navigate to "C:\Program Files\Oracle\VirtualBox\", and execute the following command (Replacing "Your VM" with your Virtual Machine's name, and System Serial with your hardware's, like "CDN29326BH", any other code may also work):

C:\Program Files\Oracle\VirtualBox>VBoxManage setextradata "Your VM" "VBoxInternal/Devices/pcbios/0/Config/DmiSystemSerial" "System Serial"

* You can use the Powershell command "Get-WMIObject win32_BIOS" or the "DMIdecode" tool to obtain "System Serial" and BIOS information.

Simple.