Generally, your ESET product is unable to scan files that are displayed as "unable to open," "error opening" and/or "archive damaged" entries (depending on product version) in the scan log due to the fact that:
Windows uses and locks certain files from startup until shutdown. These files and any others that are running in memory can't be used by or tampered with by other programs, including ESET products or potential malware. ESET does scan these files during startup and again during shutdown to ensure that they are not corrupt. If a locked file contains a threat, it will appear in red text in the scan log–files displayed in yellow are noted for informational purposes only and do not pose a threat to your system.