Below is the log view. I am using DNN 7.4.2
2015-02-17 13:49:39,593 [dev7][Thread:9][ERROR] DotNetNuke.Services.Upgrade.Upgrade - Object reference not set to an instance of an object.
System.NullReferenceException:
Object reference not set to an instance of an object.
at DotNetNuke.Services.Upgrade.Upgrade.UpgradeToVersion620()
at DotNetNuke.Services.Upgrade.Upgrade.UpgradeApplication(String providerPath, Version version, Boolean writeFeedback)
2015-02-17 13:56:07,950 [dev7][Thread:30][FATAL] DotNetNuke.Web.Common.Internal.DotNetNukeHttpApplication - System.Web.HttpException (0x80004005): Server cannot clear headers after HTTP headers have been sent.
at System.Web.HttpResponse.ClearHeaders()
at System.Web.Script.Services.RestHandler.WriteExceptionJsonString(HttpContext context, Exception ex, Int32 statusCode)
at System.Web.Script.Services.RestHandler.ExecuteWebServiceCall(HttpContext context, WebServiceMethodData methodData)
at System.Web.Handlers.ScriptModule.OnPostAcquireRequestState(Object sender, EventArgs eventArgs)
at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
2015-02-17 14:12:02,433 [dev7][Thread:41][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.InvalidCastException: Object cannot be cast from DBNull to other types.
at System.DBNull.System.IConvertible.ToDateTime(IFormatProvider provider)
at DotNetNuke.Services.Search.UserIndexer.GetUserSearch(IDataReader reader)
at DotNetNuke.Services.Search.UserIndexer.GetSearchDocuments(Int32 portalId, DateTime startDateLocal)
2015-02-17 14:51:12,581 [web-os3-08][Thread:11][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.InvalidCastException: Object cannot be cast from DBNull to other types.
at System.DBNull.System.IConvertible.ToDateTime(IFormatProvider provider)
at DotNetNuke.Services.Search.UserIndexer.GetUserSearch(IDataReader reader)
at DotNetNuke.Services.Search.UserIndexer.GetSearchDocuments(Int32 portalId, DateTime startDateLocal)
2015-02-17 14:56:23,519 [web-os3-08][Thread:5][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.InvalidCastException: Object cannot be cast from DBNull to other types.
at System.DBNull.System.IConvertible.ToDateTime(IFormatProvider provider)
at DotNetNuke.Services.Search.UserIndexer.GetUserSearch(IDataReader reader)
at DotNetNuke.Services.Search.UserIndexer.GetSearchDocuments(Int32 portalId, DateTime startDateLocal)
2015-02-17 14:58:11,401 [web-os3-08][Thread:10][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.InvalidCastException: Object cannot be cast from DBNull to other types.
at System.DBNull.System.IConvertible.ToDateTime(IFormatProvider provider)
at DotNetNuke.Services.Search.UserIndexer.GetUserSearch(IDataReader reader)
at DotNetNuke.Services.Search.UserIndexer.GetSearchDocuments(Int32 portalId, DateTime startDateLocal)
2015-02-17 15:01:03,753 [web-os3-08][Thread:17][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.InvalidCastException: Object cannot be cast from DBNull to other types.
at System.DBNull.System.IConvertible.ToDateTime(IFormatProvider provider)
at DotNetNuke.Services.Search.UserIndexer.GetUserSearch(IDataReader reader)
at DotNetNuke.Services.Search.UserIndexer.GetSearchDocuments(Int32 portalId, DateTime startDateLocal)