Hmm, most likely, the switch will not support HTTP/1.0 or HTTP/1.1 but only (obsolete) HTTP/0.9… I remember WebShield having some minor problems with this outdated version of HTTP (which is used less than rarely today)…
I’d suggest placing the address of your switch to Web Shield exception list. If that doesn’t help, you’ll have to put the address to the no-redirect list in avast4.ini (IgnoreAddress= entry in the [WebScanner] section).
Now I’ve found it in the GUI and there we have instructions for multiple addresses. On the first tab of webscanner configuration I can add the addresses separated by commas as “Ignored addresses” (or whatever it may be called in English). I don’t know why I didn’t get it to work when manually editing avast4.ini and used commas but that doesn’t matter any more.
Now it works in IE but the problem remains in Google Chrome. Any ideas how to flush the Avast-induced problem out of Chrome?