My original problem was found when Google search function with Chrome environment with Window 8.1 became unreliable as it often returned message of "Webpage is not available with error code: ERR_CONTENT_DECORDING_FAILED". The first couple of searches were fine but once this error message appeared, I could no longer use Google search. This error message is not listed Chrome technical support.
However, it appears to be caused by sending wrong codes from my PC to the search engine at Google site. After struggling, I found it may be caused by wrong LAN setting in the Internet option: i.e. (1) "use a proxy server for your LAN" was ticked, (2) "Automatically detect setting" was not ticked. It should be wrong ways around, so that I reset to default condition: (1) use a proxy server... not-ticked, (2) Automatically detect ..... Ticked. The Google search function became improved but still returned the situation of the error after several test searches. I noticed it has time dependent for the re-occurrence of the problem.
I checked the LAN setting each time and found that the setting was automatically changed back. Eventually I used "Task Manager" to check currently running software which relates to Internet connection and found software called "BrouserSafeguard with rocket Tab" as stated in one of your answers. This seems to change back the setting automatically when it scans around every minute. This caused Google search engine but other search engines such as "Bing" and "Ask Jeeves" were not affected by setting in Chrome. This is neither malware nor virus, so that my Norton anti-virus does not detect it. I uninstalled it from "Control Panel" manually and the problem was solved. I thank you for your most useful answer in this site.