[MOSS] Unknown Error when opening AreaNavigationSettings.aspx

[ISSUE]
Last week one of my colleagues contacted me about an issue he encountered. When trying to open the navigation settings page (/_layouts/AreaNavigationSettings.aspx), he encountered an "Unknown Error" (don't you just love those nice and clear errors). When opening the default page, the Quick Launch navigation on that page was also displaying errors:




[TROUBLESHOOTING]
When using the CustomErrors=Off and StackTrace=True options in the web.config, we were able to retrieve a "Object reference not set to an instance of an object" message. In the ULS logs, we found the following errors:

• Unable to retrieve the CachedObject that this ProxySiteMapNode references: /sites/test/sites/183/Pages/testpage.aspx
• PortalSiteMapProvider was unable to fetch children for node at URL: , message: Object reference not set to an instance of an object

[SOLUTION]
The quick launch navigation was changed manually and navigation items were added. Looking a little further, I found that testpage.aspx didn't exist anymore in the Pages library. Probably a user had deleted this page, causing this issue. When I recreated the testpage.aspx, the Quick Launch navigation started working again and the Navigation Settings page didn't show the error anymore.

[MOSS2007] Error during editing navigation items

[ISSUE]
When trying to edit the navigation items in a site, I get the following error message:
"The page has been modified by another author on <time>"
.....even when I am 100% nobody is changing the navigation of this site.

The reason why I was editing the navigation was because some items were having some strange URL's:
/_layouts/viewlsts.aspx?BaseType=0?BaseType=0?BaseType=0?BaseType=0

[CAUSE]
After browsing on the Internet I found that this had been caused because I used the Content and Structure Manager to move a site. SharePoint has an issue, which is causing the behaviour above.

[SOLUTION]
To solve this issue, do the following:

• Remove all of the Document Libraries and lists from the navigation by:
• Open the list/library you want to remove from the quick launch
• Click Settings > List Settings (or Library Settings)
• Click on Title, description and navigation
• Choose No for Display this list on the Quick Launch?
• Remove all corrupted navigation items
• Readd the Lists/Libraries

[MORE INFO]
Technet Forum
Windows Tech
Blog Paul Gavin

Some articles about MOSS2007 navigation

Here are some articles about navigation in MOSS2007:
HOW TO: Programmatically customize site navigation in MOSS 2007
MOSS Navigation Deep-Dive - Part 1

How to change the navigation depth of the top menu in MOSS2007

The default top navigation menu shows the mavigation structure in two levels, the first level are tabs and the second level is a dropdown menu.

It is possible to change the maximum depth of these menus. To change this default setting, do the following:
The setting can be changed by changing MaximumDynamicDisplayLevels iten in the SharePoint:AspMenu tag of the master page.

- Open the default.master page at [drive]:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\GLOBAL
- Search for "TopNavigationMenu" in the file.
- Change the property MaximumDynamicDisplayLevels to the value which you like.
- Save the file and you're done.