I have a DNN website which has a couple portal aliases.  The first is www.abc.com, and the second is abc.com (without the www), and there are corresponding host headers in IIS 6.0. 

When you go to www.abc.com, the menu for all the pages should continue to use the same alias, such as http://www.abc.com/tabid/59default.aspx, http://www.abc.com/tabid/60/default.aspx.  The problem is that sometimes, the urls in the menu suddenly start giving http://abc.com/tabid/59/default.aspx.  It's switched over to using a different alias (the one without www).  Our domain is abc, so our corporate network is setup in a way that if anyone tries to go to "http://abc.com/..." from within the network, the user gets a server not found error.  As you might imagine, this is really disconcerting when the site seems to be running fine, and then on the next click of the menu, it seems like the site went down.  If you directly tried to go to http://www.abc.com/tabid/59/default.aspx, it would still be reachable correctly.  It's only when navigating via the menus that this problem happens.  We've noticed that each time it happens, only one browser type (IE vs Firefox) will fail, and the urls will have switched on just a couple of the pages.  And the url switches for one person, anyone else who tries to get to the same pages with the same browser type will see the problem.  The other pages have the correct url and the other browser type had no problems.  However, it's a different set of pages or browser type each time.  So the next time we see this problem, it's a different set of pages where the menus will switched from www.abc.com/... to abc.com/...

This problem seems to happen intermittently every couple days, at different times of day, and we haven't been able to reproduce the problem on our staging boxes (and they have two different portal aliases).  There are no error messages logged in either the server event log or the DNN one.  We also haven't been able to set any monitoring on it because the pages render fine if going to the url directly - it's only when trying to navigate via the menus.

We're using snapsis menu.  IIS automatically recycles the worker process for this site every 29 hours. 

The short-term fix for it is to restart the application by editing the web.config file or manually killing the asp worker process for the application pool. 

We've run out of ideas for troubleshooting for a long-term fix. 

Has anyone run into this problem before or have any suggestions for what to check next?