When uninstalling Virtual Machine Additions, Windows Installer loads the corresponding MSI from %windir%\Installer\xxx.msi.
Now try this:
- find the correct MSI file (Fileproperties, or launch to see window title)
- Make a Backup of this file
- Open this MSI file in a MSI Database Editor *
- Inside the table InstallExecuteSequence delete the entries CA_CheckForRunningInsideAVirtualMachine and Error_CheckForRunningInsideAVirtualMachine
- Save this MSI
- Uninstall the Additions
* We used Orca as our MSI Database Editor.