The problem was the Add-on called prOpenAuthoring.OpenAuthor v188.8.131.52. I guess this ActiveX Control was instaled when accessing to PRPC 7.1.
Try to remove it in IE (just disable will not work). Else, just delete it (C:\Windows\Downloaded Program Files\prOpenAuthoring.ocx). While accessing to PRPC 5.5 it is asked to install again (this time v184.108.40.206)