When you uninstall RetailManager, sometimes components of the software are left behind which can interfere with future RetailManager installations. For example, even if you have uninstalled RetailManager, it still might be included in your list of installed programs.
Running a registry cleaner will remove these remaining components, and this support note explains how to do it.
Some installation issues can be fixed by running the Microsoft "Fix it" utility. This tool, freely available from the Microsoft website, diagnoses problems that can prevent installing and uninstalling programs on your computer.
Because the Fix it utility is provided by Microsoft, MYOB can't provide assistance with its use, nor take responsibility for the outcome of using this tool.