7-zip cannot open file on double click

I suggest you use the 7-Zip Command Line Version (7za.exe).

A command like the following will redirect all output (including from stderr) to Log.txt:

7za a Test.7z *.* >Log.txt 2>&1

Additionally, 7-Zip returns the following exit codes which you can use in your batch file with %ERRORLEVEL%:

0 = No error.

1 = Warning (Non fatal error(s)). For example, one or more files were locked by some other application, so they were not compressed.

2 = Fatal error.

7 = Command line error.

8 = Not enough memory for operation.

255 = User stopped the process.

Edit: If you don't want such a verbose log containing all those Compressing <filename> lines, use this command instead:

7za a Test.7z *.* | findstr /i /v "pavlov scanning compressing" >Log.txt 2>&1

(The findstr command with switches above excludes all lines containing the words within quotes.)

You can do this from within the program itself. Simply launch the 7-Zip File Manager as Administrator (this is important), and then click on the Tools menu and select Options. Here you can set your file associations for many types, not just the .7z extension.