Periodically ViewState verification fail

Hi I hope you can help me with this problem:

Checking the event viewer of a Web Application I have noticed that periodically happens a ViewState Verification fail. It happens several times by day on a diferent .aspx pages. Sometimes it causes an error and the user loses his data, but other times apparently user can continue using the application.

This is the event registered ( I have changed the computer name and the path data, but it's not importante for the question)

COMPUTER_NAMEEvent code: 4009
Event message: Viewstate verification failed.Reason: The viewstate supplied failed integrity check.Event time: 10/8/2006 6:54:00 PM
Event time (UTC): 10/8/2006 4:54:00 PM
Event ID: 78a9d00b907b4edab1ac37665fa3175c Event sequence: 447 Event occurrence: 2 Event detail code: 50203
Application information:
Application domain: /LM/W3SVC/250184202/Root/ApplicationPath-1-128047877472787699
Trust level: Full
Application Virtual Path: /ApplicationName Application Path: D:\Directory\www\ ApplicationName \ Machine name: COMPUTER_NAME
Process information: Process ID: 2916
Process name: w3wp.exe
Account name: NT AUTHORITY\NETWORK SERVICE
Request information:
Request URL: http://ApplicationName /ApplicationForm.aspx
Request path: ApplicationName /ApplicationForm.aspx
User host address: 80.66.205.47User: USER@dotnet.itags.org.application.com
Is authenticated: True
Authentication Type: Custom
Thread account name: NT AUTHORITY\NETWORK SERVICE
ViewStateException information: Exception message: Invalid viewstate. Client IP: 80.98.185.47
Port: 16528 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.0.7) Gecko/20060909 Firefox/1.5.0.7 PersistedState: ML0cSytZ3NNxTv6HMBICK (… Here appears lines and lines of the viewstate dumped) … LecAy+p3fFVSdi7LZEE= Referer: http://ApplicationName /ApplicationForm.aspx
Path: ApplicationName/ApplicationForm.aspx aspx
Custom event details:10/8/20066:01:15 PMASP.NET 2.0.50727.0InformationWeb Event 1316N/A

Any help would be appreciated

Thanks

There are a lot of possible causes for this issue. You can take a look this KB:

Troubleshooting the "View State is invalid" error with ASP.NET

Hi expert, I am also having this type of error. The first error from different user is this one:

Event code: 4009

Event message: Viewstate verification failed. Reason: The viewstate supplied failed integrity check.

Then another error, from different user is this:

Event code: 4005

Event message: Forms authentication failed for the request. Reason: The ticket supplied was invalid.

Please advise. Thanks.