As other users have reported, I, too, have been unable to update the CIS 5.10 virus database the past couple of days. The incremental database updates are downloaded successfully and I can see the incremental download is decompressed successfully in the SCANNERS folder (extension of $$$). However, it appears there is a problem in merging the updates with the virus database and then subsequently copying the previous database version to the REPAIR folder.
I have read other postings on this issue indicating that a user should upgrade to the latest version of CIS, 7.0.315459. That’s not really an answer. I would like to continue to use version 5.10.228257. Having an older computer, I much prefer CIS 5.10 since it has only 2 processes, not 4, like CIS 7.0, and resource consumption is somewhat lower. I hope COMODO is not forcing users of earlier versions of CIS to migrate to the latest version by not making virus updates available to earlier versions of CIS.
Version 7 uses the same database as v5.8 and newer. You can keep on using 5.10 for quite a while. Even if the database format would change then history shows that Comodo will keep on providing older databases. At this moment the v4 database is still provided for.
When deleting the bases.$$$ does not help try stopping and starting Comodo Internet Security Helper Services under Services. Services can be found in Control Panel → Administrative Tools.