Value cannot be null. Parameter name: value

System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> 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, DateTime absoluteExpiration, TimeSpan slidingExpiration)
   at MyStateManager.addItem(StateStorageType aStorageType, String aKey, Object aValue, Double aHoursToStoreInCache) in d:\hosting\11290390\html\App_Code\MyStateManager.cs:line 95
   at MyStateManager.addItem(StateStorageType aStorageType, String aKey, Object aValue) in d:\hosting\11290390\html\App_Code\MyStateManager.cs:line 68
   at MyCachedData.getAllCategories(GenericDatabaseInfo aDatabaseInfo, Boolean aUseCachedData) in d:\hosting\11290390\html\App_Code\MyCachedData.cs:line 825
   at MyCachedData.getAllCategoriesAsList(GenericDatabaseInfo aDatabaseInfo, Boolean aUseCachedData) in d:\hosting\11290390\html\App_Code\MyCachedData.cs:line 4066
   at MyCachedData.getOnlyCategoryGroupings(GenericDatabaseInfo aDatabaseInfo, ResultsOrderByTypes aOrderByType, SearchParameterTypes aParentFieldType, String aParentFieldValue, Boolean aUseCachedData) in d:\hosting\11290390\html\App_Code\MyCachedData.cs:line 4253
   at MyCachedData.getOnlySimilarCategoryGroupings(GenericDatabaseInfo aDatabaseInfo, ResultsOrderByTypes aOrderByType, SearchParameterTypes aParentFieldType, String aParentFieldValue, SearchParameterTypes aCurrentItemFieldType, String aCurrentItemFieldValue, Boolean aUseCachedData) in d:\hosting\11290390\html\App_Code\MyCachedData.cs:line 4315
   at view_page.getRelatedItems(SearchParameterTypes aCategoryFieldType, String aCategoryFieldValue, SearchParameterTypes aItemFieldType, String aItemFieldValue, Boolean aUseCachedData, Int32 aNumItemsToDisplay) in d:\hosting\11290390\html\view_page.aspx.cs:line 135
   at view_page.Page_Load(Object sender, EventArgs e) in d:\hosting\11290390\html\view_page.aspx.cs:line 53
   at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.HandleError(Exception e)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest()
   at System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context)
   at System.Web.UI.Page.ProcessRequest(HttpContext context)
   at ASP.view_page_aspx.ProcessRequest(HttpContext context) in c:\windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\root\c142425c\57568e4e\App_Web_3uprbrwu.6.cs:line 0
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)