Cannot unpack .RAR file(s)

I find that after downloading both the source and no-source .rar files (ver. 4.20), I get an error message ("The archive is either in unknown format or damaged" when using WinRAR, and "Cannot open file" when using 7-zip).  I cannot unpack them or even view them.  Any ideas?

I don't have a problem using 7-zip.  Unblock the .rar file first.  Then use the 'open archive' file menu option rather than trying to double-click the .rar file.

That worked.  Thanks a lot.

How do I unblock the rar file? I don't see any option for unblock when I right-click the rar, and I can't load into winzip.
I get:
Cannot open file: it does appear to be a valid archive.

In windows, right-click, select Properties, it should be in lower right (either a button, or a checkbox)

You need 7-Zip to unpack rar.

Use win rar.