we found a similar problem with our custom install.
The "unfriendly" error is as follows:
Value cannot be null.
Parameter name: value
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.ArgumentNullException: Value cannot be null.
Parameter name: value
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[ArgumentNullException: Value cannot be null.
Parameter name: value]
System.Web.Caching.CacheEntry..ctor(String key, Object value, CacheDependency dependency, CacheItemRemovedCallback onRemovedHandler, DateTime utcAbsoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, Boolean isPublic) +3599655
System.Web.Caching.CacheInternal.DoInsert(Boolean isPublic, String key, Object value, CacheDependency dependencies, DateTime utcAbsoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, Boolean replace) +88
System.Web.Caching.Cache.Insert(String key, Object value) +83
DotNetNuke.Services.Cache.FileBasedCachingProvider.FBCachingProvider.Insert(String CacheKey, Object objObject, CacheDependency objDependency, DateTime AbsoluteExpiration, TimeSpan SlidingExpiration, CacheItemPriority Priority, CacheItemRemovedCallback OnRemoveCallback, Boolean PersistAppRestart) +134
DotNetNuke.Services.Cache.FileBasedCachingProvider.FBCachingProvider.Insert(String CacheKey, Object objObject, CacheDependency objDependency, DateTime AbsoluteExpiration, TimeSpan SlidingExpiration, Boolean PersistAppRestart) +70
DotNetNuke.Common.Utilities.DataCache.SetCache(String CacheKey, Object objObject, TimeSpan SlidingExpiration, Boolean PersistAppRestart) +72
DotNetNuke.Entities.Portals.PortalController.GetPortal(Int32 PortalId) +280
DotNetNuke.Entities.Portals.PortalSettings.GetPortalSettings(Int32 TabId, PortalAliasInfo objPortalAliasInfo) +121
DotNetNuke.Common.Globals.GetHostPortalSettings() +214
DotNetNuke.Common.Globals.GetPortalSettings() +79
DotNetNuke.Authentication.ActiveDirectory.HttpModules.AuthenticationModule.OnAuthenticateRequest(Object s, EventArgs e) +67
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64