I still get those and I don't think it is such a good idea to set protection to 'none' though this seems only valid for IE. I have been reading How To: Configure MachineKey in ASP.NET 2.0 (PAG Documentation): http://msdn.microsoft.com/library/en-us/dnpag2/html/PAGHT000007.asp?frame=true to better understand this mechanisme. It is cleary stated that you should only change the default values if one is using a webfarm. In this article the following settings are defined as default:

validation="SHA1" decryption="Auto" />

If I look in the release.config decryption is set to 3DES and not to 'Auto'. What is the reason for this?

I set protection to 'none' and that does not make any difference either:

Event Type: Information
Event Source: ASP.NET 2.0.50727.0
Event Category: Web Event
Event ID: 1315
Date:  4/2/2006
Time:  1:35:05 PM
User:  N/A
Computer: SERVER
Description:
Event code: 4005
Event message: Forms authentication failed for the request. Reason: The ticket supplied was invalid.
Event time: 4/2/2006 1:35:05 PM
Event time (UTC): 4/2/2006 11:35:05 AM
Event ID: c755cdf2ac104274b345b1ed0df284b7
Event sequence: 52
Event occurrence: 5
Event detail code: 50201
 
Application information:
    Application domain: /LM/W3SVC/1697751234/Root-1-127884510663658654
    Trust level: Full
    Application Virtual Path: /
    Application Path: D:\Dotnetnuke\
    Machine name: SERVER
 
Process information:
    Process ID: 4316
    Process name: w3wp.exe
    Account name: NT AUTHORITY\NETWORK SERVICE
 
Request information:
    Request URL: http://www.smallbizserver.net/Default.aspx
    Request path: /Default.aspx
    User host address: 82.138.202.128
    User: 
    Is authenticated: False
    Authentication Type: 
    Thread account name: NT AUTHORITY\NETWORK SERVICE
 
Name to authenticate: 
 
Custom event details:

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

Hi Cathal,

Thanks for your time and effort to help me. I just finished a virtual machine with Windows Server 2003 R2 + SQL 2005. I have copied all stuff there and I do not have the issue.

Probably next week I will get new hardware and I will install Windows Server 2003 R2 x64 on that. I will move the site to that new hardware hopefully also end of next week after I have done some testing. One last question....are there any quirks running DNN 4.0 on x64 machine?

BTW, I will keep the old machine and spend some time on it trying to find the cause of this. Just as a learning experience. I just can't stand this...