For various reasons, installutil.exe can experience errors when uninstalling a Windows service based on a .NET assembly and the service never gets uninstalled. I ran across this problem recently (for the nth time!) and I wanted to post my findings.
To uninstall the service, simply delete the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MySvc
where "MySvc" is the name of the service to uninstall. After that, reboot and all should be well.
Note: If you search the registry, you may find the key listed under other sections, such as "ControlSet001". I left these alone and only deleted the key under CurrentControlSet.
To uninstall the service, simply delete the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MySvc
where "MySvc" is the name of the service to uninstall. After that, reboot and all should be well.
Note: If you search the registry, you may find the key listed under other sections, such as "ControlSet001". I left these alone and only deleted the key under CurrentControlSet.