There is a problem with Windows 98, Windows Installer v2 and NAI VirusScan 4.5.x.  What sometimes happens is that the antivirus fails to load at boot time as Windows 98 service.  The error appears before the logon screen and leaves your computer vunerable to virus attack.

The errors that you are likely to see are as follows.

• "VirusScan could not start due to missing or outdated AVSYNCH.DLL libraries, please reinstall Windows Installer (MSI) 2.0"
• "VirusScan could not start due to missing or outdated AVSYNCH.DLL libraries, please reinstall the program"

The cause of this error is the Microsoft Windows Installer Technology (MSI) version 2.  Windows Installer contains some complex but clever technology that allows programs to check that all the files and shortcuts are in the right place, if they are not then the application is repaired acording to the specification of the MSI file.

Most application that use MSI technology will be packaged with the Windows Installer services (instmsi.exe) this is installed/updated automatically - you don't have a choice in the matter. 

Unfortunately our error is most commonly caused by the SoftEase Easiteach application, that uses the MSI2 format to install, although I must add that other applications such as Office XP will also upgrade the Windows Installer service.

The Fix

The solution, although not ideal is to downgrade the Windows Installer to an older version, the error is then magically resolved.

1. Run the following from the command prompt: msiexec /unregister
2. Delete msi.dll, msiexec.exe and msihnd.dll files from the system folder (usually c:\windows\system)
3. Restart Windows
4. Run the INSTMSI.EXE program from your AntiVirus 4.5.1 CD-ROM to reinstall the Windows Installer Service.
   

 Repeat this process for all affected machines.