I could use some help please. I use UltraVNC as a complementary module in a "language laboratory" style application. It enables the teacher to see the students' screens while they are working. The teacher can also hear each student's oral work (but this part of the application is independent of UVNC).
Until now I have been using UltraVNC version 1.0.8.0 and everything has been fine. On my network I have many versions of Windows(XP, Vista, Windows 7, Windows

I have a problem with the XP computers. When I try to run vncviewer version 1.1.9.1 on an XP machine I get this error message: "vcnviewer is not a valid Win32 application"; Is something missing like a dll for example? If I run vcnviewer.exe version 1.1.9.1 on a Vista or Win 7 machine everything goes as planned.
I would be grateful for any enlightenment.
P.S. I have also posted this on the French Forum if you would prefer to reply in French.