Users of Kaspersky Antivirus have been complaining since the end of January that when they open Chrome, they see alerts stating that there is a problem with a self-signed certificate. Google employee states that there has been an increase in Chromecast discovery issues from Windows users and that it appears to be related to antivirus software. Users have discovered they can either disable SSL scanning or find the IP address for the Chromecast device and add it as an exclusion to the SSL scanning engine. Google has stated that they have reached out to Google to resolve the issue.
Source: https://www.bleepingcomputer.com/news/security/kaspersky-av-having-certificate-conflicts-with-google-chromecast/