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When i first start a virtual machine in virtualbox 5.1.38 before install windows 7 on the virtual machine i am getting this problem

A problem has been detected and windows has been shut down to prevent damage to your computer.

If this is the first time you've seen this stop error screen,
restart your computer. If this screen appears again, follow these steps:

The BIOS in this system is not fully ACPI compliant. Please contact your system vendor for an updated BIOS.

Technical information:

STOP: 0x000000A5 (0x00000011, 0x00000007, 0x80f6c8b8, 0x20100528)


How can i fix it

Is your host Windows 7 and when you try to start a VM you get a BSOD? Did I understand it right? What's the guest?

Upgrade to VirtualBox 5.2.22 which is the latest version. See if that changes the situation.