1. System.Web.Script. Serialization. JavaScriptObjectDeserializer. DeserializePrimitiveObject
After google a while, and find a lot of same errors in DNN forum without a solution. and for my case this is only happened to FF old versions.
UserAgent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; MRA 4.6 (build 01425))
After I upgrade my firefox to the latest version. It solved. But I could not ask every user to upgrade their FF, right?
Btw, my error occurs at: DotNetNuke.UI.WebControls.DNNMenu.LoadPostedJSON()
2. Dashboard link throw module file not found error.
Solution: goto Host -> Module Definations -> Edit "Dashboard". make sure you "Module Cotrol" section looks like below:
3. iFinity.DNN.Modules.GoogleSiteMap not working. The googlesitemap.axd return 0 urls.
Reason: the portal does not have a default language. I donot know why the default language is missing after upgrade. 
Solution: Login as host account. Admin -> Languages -> Edit language
make sure the "Enabled" checkbox is checked.
Go to Admin -> Site Settings -> Advanced Settings -> Other Settings: Make sure the Default Language dropdownlist has selected some value.
