Antivirus scanner cannot read/scan some files
Your anti-virus program reports that some files could not be scanned, usually when conducting a manual scan of the entire hard disk.
This is quite normal. In Windows there are always a number of files that are kept open by the operating system and are not available to be scanned.
Some examples of files that cannot be scanned are:
BUT: while the inability to scan certain files is normal, it is also true that certain type of malicious files cannot be scanned because they are designed to be inaccessible. Normally when a program executes, the original files (.exe or .dll) are closed and can therefore be scanned even when the program is running. So any files such as .exe or .dll which cannot be scanned can be an indicator of malicious intent since it is not normal to keep the file locked.
Therefore there is a value in regularly examining scan logs for files of this type.