Can't run 16-bit Windows program

This application is not supported by Microsoft Windows NT. I get this error message on an NT 4 machine when I try to install acrobat reader 4.05. There is nothing wrong with the acrobat file I use it to install reader on all the machines. I've reinstalled SP6a and windows installer but to no effect. I had the same error installing Norton 2000 on same machine but found a work around on norton site. Could find nothing useful on adobe site or technet. How do I install reader 4.05 without reinstalling windows.
P.S acrobat reader 3.01 installs and uninstalls without any problems
Peter