I recently ran into an issue on a computer that had ESET NOD32, with an error message for being unable to scan POP3 or HTTP.
During the troubleshooting process for this error we uninstalled the client and tried to re-install it. We ran into issues saying that there was another installation already in progress and that the ESET client kept rolling back and not completing the re-installation.
I was finally able to track the issues back to the Base Filtering Engine service having been removed by malware that was on the machine. After cleaning the malware off of the machine using the ESET online scanner I was able to follow http://kb.eset.com/zap/SOLN2861 and get the service working again. Once the BFE service was working the installation went through without a hitch.
One thing that might help tracking this problem down is the following error in the event logs:
Log Name: System
Source: Service Control Manager
Date: 5/25/2012 8:25:56 AM
Event ID: 7003
Task Category: None
Computer: Computer Name
The epfwwfpr service depends the following service: BFE. This service might not be installed.