Adobe Acrobat 8.0

We operate in a Novell 5.1 environment with Adobe Acrobat 4.0, upgraded to 5.0, then, to 6.0 then, to 7.0 without errors over the past several years. We just received 8.0 and have upgraded a dozen people with 8.0 pro however, of the dozen people about 1/4 are having problems. Once a pdf in Acrobat 8.0 is opened an then closed the program freezes and returns an error. HOWEVER, if with uninstall the Netware client (4.91 sp2) and then duplicate the process, it does not return an error. Any ideas???