This is not an issue with the navigation bar (breadcrumbs navigation it is called). If you open the URL directly, it will fail too.
You'll have to check the server PHP error logs to see what is going on. The page is crashing for some reason. PHP responds with a white page in such case.
You can also enable the module "Event Logging" that is bundled with Phorum. After enabling the module, trigger the problem. Then go to the settings of the Event Logging module. From within the settings, you will be able to view the event logs. Check if anything interesting is being logged in there.
Maurice Makaay
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Edited 1 time(s). Last edit at 10/17/2010 05:02PM by Maurice Makaay.