I've tried all solutions referenced in this thread and others.  I'm at a total loss as to why my fresh DNN portal makes its children toss their cookies.  If one wades through the dnnforums, there are people regularly afflicted with the issue.  I'll keep trying to think of a solution.  It seems that Firefox is not totally immune from this issue, as evidenced by going to the Skins screen where image links are broken.  One can easily browse directly to those images under the _default folder, but DNN seems to get in the way and deny it as a security matter. 

Well, we've got a 4.3.7 which still has the logout problem.
In this case it involves calling a .aspx file in an iFrame.
It seems the cookie of the administrator gets lost.
Any ideas to resolve this are welcome.

On our 4.0.3 install it has been happening for about half a year now.
Indeed when clicking edit buttons, going to setting pages, etc. etc.

I've seen that the issue at least occured since version 3.2.0.
We have had a lot of complaints about this issue.
I think this is a REAL BIG problem for DNN, but I guess the core members see it differently.

My issue is not that the application restarts.

The problem is that administrators of a child portal will be checked for authentication while doing certain actions.
DNN searches through the users of the parent portal, and can't find the user (because it only is a user in the child portal). So the administrator get's thrown out of the system, and gets redirected to the login page.

Sometimes there might be other reasons for loosing the authentication. For example when you use an aspx file in an iFrame, your cookie get's thrown away. So the next page you visit, you get logged out.