wz z wrote
[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) +3503375
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, CacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback) +81
DotNetNuke.Services.Cache.FileBasedCachingProvider.FBCachingProvider.Insert(String CacheKey, Object objObject, CacheDependency objDependency, DateTime AbsoluteExpiration, TimeSpan SlidingExpiration, CacheItemPriority Priority, CacheItemRemovedCallback OnRemoveCallback, Boolean PersistAppRestart) +160
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() +216
DotNetNuke.Common.Globals.GetPortalSettings() +79
DotNetNuke.Authentication.ActiveDirectory.HttpModules.AuthenticationModule.OnAuthenticateRequest(Object s, EventArgs e) +48
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64
This error appears to have nothing to do with installing Optional Skins - Note that it is triggered by - DotNetNuke.Authentication.ActiveDirectory.HttpModules.AuthenticationModule.OnAuthenticateRequest.
I would expect that in this case even if there is some skins to install then the error would occur.