Once upon a time, I tried unistalling MSE because it was conflicting with other antivirus/malware programs.

Afterwards, I found I was unable to download any files from the internet, I would get an error saying "Virus scan failed, file DELETED".

I assume this was an issue with MSE, so I decided to reinstall it.

I uninstalled all my other antivirus/malware software, ran Ccleaner, downloaded MSE from a FRIEND's computer and ATTEMPTED to reinstall it on my machine.

The MSE INSTALLER comes up with an error about not being able to find or access epp.msi, and neither can I.

After getting frustrated by the snipe hunt on Microsoft's "TECH support" forum, I decided to try here.First, follow this link and download the removal tools for ALL of the listed programs you have installed or have previously had installed, even if you think you've already uninstalled them, including MSE:
http://experts.windows.com/w/experts_wiki/156.aspx

Next, make sure all Windows updates are installed and any important data is backed up.

When you're ready to install again, go to this link and download MSE and install again:
http://www.microsoft.com/security_essentials/

Note for the future: Never have more than one real-time antivirus running at the same time. Despite the logic that more protection is better, having more than one antivirus suite running at a time can and likely will cause a conflict. Install one real-time AV product and one firewall product (if your AV doesn't provide a firewall service).

Some items are exempt from this rule, like Malwarebyte's Antimalware since it doesn't do real-time scans. Always check for programs that might possibly conflict. If you aren't sure, you can always come back and ask. Nothing else has worked, so I went back to the earliest restore point and so far that seems to have fixed my issue. Hopefully re-installing windows updates will not break it again.