Windows 7 32 bit activation loss after VM reboot

Dear All,

My client whose system is still an old VMWare system (Vphere 5.5/EXSi 5.5), running windows 7 32bit VM, recently report that the windows 7 become non genuine after a scheduled reboot. What would be the cause and how to fix the issue so the windows 7 32 bit VM can resume genuine version?