This issue occurs if there are issues with the underlying storage, which results in subsequent writes to the NVRAM file to fail.
The NVRAM file of a virtual machine stores the state of the virtual machine's BIOS settings. When you modify the BIOS settings, ESXi makes the changes persistent by storing them in the NVRAM file. If there are any issues with the underlying datastore on which the virtual machine's configuration files are stored, it results in failures while writing the new BIOS settings to the NVRAM file of the virtual machine.