Cannot Access Windows Installer after Uninstall HELP!!!!!!

Alright, I'm packaging an app for work and finally got every function working properly after countless hours of troubleshooting. Then I tested out the uninstall. After I install the app, everything works great, I can install/uninstall other apps no problem. But if I uninstall the original app, then I cannot install anything else unless I reboot which is unacceptable. The original setup does not require a reboot after uninstall. If I do try to install another app without a reboot then I get the error "Windows installer service could not be accessed...." If I try to manually start the windows installer service the I get the error message: "Could not start the Windows installer service on the local computer. Error 1018: Illegal operation detected on a registry key that has been marked for deletion." I have google this to no end, tried to use procmon, and have the uninstall log if anyone wants me to post it. I'm fairly new to packaging apps and am pleading for some of you experts to help me figure this out. Thanks in advance.
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which version of windows do You use?
if You use win xp the problem is probably with Windows installer service,try to stop and start it .I agree with You this is unacceptable so may need to check with the Install program vendor ,it should start the service automatically if it's stopped .
But first check if You're using admin permissions,otherwise You'll never have rights to write the registry - that explains it.

More info on You error:
rich872Author Commented:
After several hours more of troubleshooting, trying everything posted here and more,I just started over.  There were two setups to install into and there were multiple updates.  I used snapshots instead of installation monitoring and rebooted after each setup was complete and again after the updates then took the final snapshot.  This solved my issue with windows installer.  There were a few more bugs but I was able to get all those resolved as well using procmon.  Thanks for trying to help, much appreciated.

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