<at least, for me>
Norton Internet Security, Personal Firewall, requires custom internet access program entries for !both! iTunes.exe and iTuneshelper.exe.
iTunes was already there, but iTuneshelper was not. Adding iTuneshelper solved the 403 and 555 problems first time out!
Here's a URL to Symantec support for instructions on how to add iTuneshelper:
http://symantec.atgnow.com/consumer/resultDisplay.do?gotoLink=69&docType=1000&co ntextId=3837%3A69.167&clusterName=ConsumerCluster&contentId=b50a6981-6a2a-4e1d-b 49f-4dcfc813c053&responseId=1247c80604ccad04%3A1b1fbf4%3A106ecce5bd1%3A-3fa6&gro upId=1&answerGroup=1&score=900&page=http%3A%2F%2Fservice1.symantec.com%2Fsupport %2Fnip.nsf%2Fpfdocs%2F2005092908351036&result=0&excerpt=iTunescannot+connect+to+the+Music+Store+or+Shared+Music+after+installing+Norton+Intern etSecurity&resultType=5000#
<woa that's a long one!) You'll need to copy it carefully into your browser address bar> Here are the basic instructions copied from there:
To set up Norton Internet Security or Norton Personal Firewall to allow iTunes to connect to the Internet, check for a program rule for iTunes. Set the rule to permit all. If no program rule exists for iTunes, add a rule.
To check for an existing program rule for iTunes
Start Norton Internet Security or Norton Personal Firewall.
Click Personal Firewall.
Click Configure.
On the Programs tab, scroll through the Manual Program Control window until you find iTunes.
Do one of the following:
If you find iTunes, then verify that the Internet Access setting is Permit All. If it is set to Deny, then set it to Permit All.
If you do not find iTunes in this list, then you must add a program rule to allow iTunes to access the Internet.
To add a program rule for iTunes
Open Norton Internet Security or Norton Personal Firewall.
Click Personal Firewall.
Click Configure.
On the Programs tab, click Add.
In the Select a program window, browse to iTunes.exe.
Click Open.
In the Program Control window, click Permit All, then click OK.
Repeat steps 47 for iTunesHelper.exe.
Click OK.
Good luck! -- JH
