Just done a full system scan and I got the above message together with the list of files concerned. It said they could not be read as “archive is password protected”. I could not do anything with the files like put them into the chest. Can anyone give me any advice?
Just do nothing. This is just a information that these files cannot be scanned since they are password protected.
And they cannot do any harm to your computer. When they are executed they will be scanned. 
short answer, nothing to worry about
Some files can’t be scanned is this forums most frequently asked question so plenty info if you forum search
Sorry I will look in the index then. However I have not made and password protected files 
many programs protect there files with passwords that only that program know… feks adobe
files that can not be scanned does not mean they are infected, just that avast could not scan them for whatever reason avast give…it is just a scan error report
and they will be scanned by the real time protection when the program that use those files unpack them
Windows Updates will have some files like this as well… from my experience on my setups.