Opera problem with asp.net site: System.Web.HttpException: state information is invalid

Hi,
I'm seeing this error happening on ASP.NET 2.0 sites with a slightly different error message ("Validation of viewstate MAC failed.") which basically boils down to the same error you're getting.

Analyzing the hostnames of the requests generating such errors, most of the time the hostname seems to indicate the request came from a hosted environment, eg. not a person's home or office pc or anything. My guess is this error is caused by webcrawler apps that don't resend the viewstate in a request like they're supposed to, possibly in an attempt to gain access to your site. In other words, I think these errors are hack attempts using software that does not sufficiently imitate browser behavior.

There are many situations that can cause this. I had a look at some MS articles.

- Browsers that cannot support hidden fields very well - http://support.microsoft.com/kb/831150
- Small numbers - http://support.microsoft.com/kb/812399
- Your viewstate is too big. Some browsers can't handle that
- There is some network error. The viewstate information was corrupted on the way, but I doubt it in your case cos problem only exists with Opera
- If hosted on a web farm http://support.microsoft.com/default.asp...

Also have a look at this, u may find some info in there to help you
http://aspalliance.com/articleViewer.asp...

thanks for your answers, guys, and sorry for not getting back quicker.
It is not a web crawler problem, notpingu, I'm quite sure about that.
nidhi, i've been looking at the solutions you provided links for and i think it's a problem of the viewstate being too big. this is not so easy for me to fix, so right now i've implemented the serverside viewstate as described in the last link you provided. this seems to do the trick.

Here I have a good recommend for you: Tuneup360 and Norton system work, but the latter one is a little bit difficult. For the beginners, Tuneup360 is a good choice