Unable to change Navigation Settings

Error message from ULS log when trying to modify Navigation Settings (Site Settings > Navigation):

Unable to retrieve TopNavigationBar SPNavigationNodeCollection from Web at: <url>. The SPNavigation store is likely corrupt.

Run the following db script:

INSERT INTO [Cotent_db].[dbo].[NavNodes]
 ([SiteId], [WebId], [Eid], [EidParent], [NumChildren], [RankChild],[ElementType], [Url],
 [DocId], [Name], [DateLastModified], [NodeMetainfo], [NonNavPage], [NavSequence], [ChildOfSequence])
SELECT DISTINCT SiteId, WebId ,1002 ,0 ,0 ,1 ,1 ,'', NULL, 'SharePoint Top Navbar',getdate() ,NULL ,0 ,1 ,0
 FROM [Cotent_db].[dbo].[NavNodes] WHERE WebId NOT IN (SELECT WebId FROM [Cotent_db].[dbo].[NavNodes] WHERE Eid = 1002) 

Thanks to:
http://bimoss.wordpress.com/2009/09/29/unable-to-modify-global-navigation-add-headinglink/

"Cannot uninstall Language Pack" and Unexpected System.NullReferenceException when trying to access the web site

How to fix this error

The message "Cannot uninstall Language Pack" appears when doing Uninstall-SPSolution and an Unexpected System.NullReferenceException appears when trying to access the web site. This error may only be present on one of the servers in a farm.

1. Stop the SharePoint Timer Service (OWSTIMER).
2. On the problem server, navigate to:
1. Windows Server 2003 location: Drive:\Documents and Settings\All Users\Application Data\Microsoft\SharePoint\Config\GUID and delete all the XML files from the directory.
2. Windows Server 2008 location: Drive:\ProgramData\Microsoft\SharePoint\Config\GUID and delete all the XML files from the directory.
3. Delete all the XML files in the directory or sub directories, not the .INI file.
4. Open the cache.ini with Notepad and reset the number to 1. Save and close the file.
5. Start the service on the server and wait for XML files to begin to reappear.
6. IIS Reset