VBScript Runtime Error : Unknown runtime error: 'Application.DisplayAlerts'

Question

When running VBScript, the Runtime Error appear

"Unknown runtime error: 'Application.DisplayAlerts'
Code : 800AC472

the line in the vbscript where it stopped is
xlApp.Application.DisplayAlerts = False

It happened randomly, e.g. once in a week and it did not happen every time run manually or under scheduler.

May I know if anyone can shed some lights on that ?

thanks !