I'm in charge with customizing a MyltiStore 9.1.0.0 site.
There is a strange problem with the login / logout process.
Sometimes when you try to log in, a message stating that "Signin is complete, please wait..." appears on the page. However the login does not take place, i.e. the initial page is just refreshed. If you use Fiddler2 (http://fiddler2.com) to inspect the cookies from the request header, you can see that the ASPDNSFGUID value is missing. As far as I can see from the controls\Signin.ascx.cs code (lines 226 - 229) it seems that the FormsAuthentication.SetAuthCookie method does not work (?).
Something similar happens when you try to log out - click on the Logout link and you'll not be logged out.
The behavior is intermittent (I use IE10 and Mozilla Firefox 22.0, I tried to clear the cookies, etc...) and unfortunately I cannot find anything that may have caused it. I've also deleted the temporary .NET files, but this did not help.
This happens only on the live server. My customer also has a staging server on a different machine, and never encountered the strange behavior in the test environment. I also have a copy of the site on my dev machine, and it works fine.
Is there anything I can do to fix the "bug"? Since this happens only on the live server, should I move the site on a similar new machine?