I have a 64 bit Win7 Ultimate guest VM installed on 64 bit Ubuntu 20.04.4 LTS box. Install of the Guest Additions for 6.1.32 VBox fails with "ERROR (800b0100) No signature was present in the subject".

A msg at the top of the install dialog says "Installation Aborted. Setup was not completed successfully."

Any suggested fixes/work arounds? The VM is completely useless without access to the host file system. The postage stamp display is no panacea either.