I installed new forum software 2 weeks ago on current DNN version (4.7.0). Worked just fine. Thanks! I was getting significant number of exceptions, but overall worked well

Suddenly, without any change from me, 100's of exceptions. And the first page of the Aggregate forum shows parts of the first thread, but stops when writing the forum user. and generates an exception (value cannot be null). Evidently, the forum user returns null and DNN generates an exception and stop generating the page, hence the bizarre looking page. Should I downgrade DNN to 4.6.2 or is there another solution.

AssemblyVersion: 04.07.00
PortalID: 0
PortalName: SQLNotes
UserID: 5
UserName: PPL
ActiveTabID: 54
ActiveTabName: Forums
RawURL: /Default.aspx?tabid=54&forumid=-1&scope=threads
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.sqlnotes.net/Default.aspx?tabid=54
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; fr; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9 Creative ZENcast v1.02.10
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 5a410d8a-210a-4ec4-a62c-7c21e3b3c2b8
InnerException: Value cannot be null. Parameter name: value
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Web.Caching.CacheEntry..ctor
StackTrace:
Message: System.ArgumentNullException: Value cannot be null. Parameter name: value at System.Web.Caching.CacheEntry..ctor(String key, Object value, CacheDependency dependency, CacheItemRemovedCallback onRemovedHandler, DateTime utcAbsoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, Boolean isPublic) at System.Web.Caching.CacheInternal.DoInsert(Boolean isPublic, String key, Object value, CacheDependency dependencies, DateTime utcAbsoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, Boolean replace) at System.Web.Caching.Cache.Insert(String key, Object value, CacheDependency dependencies) at DotNetNuke.Services.Cache.FileBasedCachingProvider.FBCachingProvider.Insert(String CacheKey, Object objObject, Boolean PersistAppRestart) at DotNetNuke.Common.Utilities.DataCache.SetCache(String CacheKey, Object objObject) at DotNetNuke.Modules.Forum.ThreadInfo.GetThreadInfo(Int32 ThreadID) at DotNetNuke.Modules.Forum.Threads.RenderThreadInfo(HtmlTextWriter wr, Boolean AggregatedView)
Source:
Server Name: SINGLE25: