I receive the following exeption every day in my event log, what is wrong? DNN 4.4.1

File System Synchronization failed. System.NullReferenceException: Object reference not set to an instance of an object.
   at DotNetNuke.Services.FileSystem.FolderController.GetMappedDirectory(String VirtualDirectory)
   at DotNetNuke.Entities.Portals.PortalInfo.get_HomeDirectoryMapPath()
   at DotNetNuke.Services.FileSystem.SynchronizeFileSystem.Synchronize()
   at DotNetNuke.Services.FileSystem.SynchronizeFileSystem.DoWork()

Sten

It has been enabled, but now I have unabled it to see if it helps. But no change, I still recive the messages in the event log?

In my case, it was the way I installed PageBlaster ... if you are using PageBlaster, and it is using the /Portals/_default/Cache folder as its cache-folder, then create a "Cache" folder at the DNN root, and alter the pageblaster config

        cache-folder="/Cache"

this is for the free version of PageBlaster. That took care of all my problems.

Edit: Additionally, I deleted the folders below the /Portals/_default/Cache folder which were created by PageBlaster as well as any pb.webinfo file in /Portals/_default/Cache ... not visible in FileManager, had to do this at the filesystem level.