I recently upgraded a portal to the latest 5.6.1 version.  Everything is working properly, but when I edit a few select pages and click save to any module, when it returns to the page I get an "Object instance not set to an instance of an object".  Checking the Event Viewer log I see the following two errors and not having much luck figuring out a solution.  It isn't causing my portal to crash, just annoying seeing the message after editing.  Any help would be greatly appreciated.

AssemblyVersion: 5.6.1
PortalID: 0
PortalName: LanczGlobal Member's Only
UserID: 1
UserName: host
ActiveTabID: 88
ActiveTabName: ABL Personal
RawURL: /mo/Default.aspx?tabid=88&ctl=Edit&mid=883
AbsoluteURL: /mo/Default.aspx
AbsoluteURLReferrer: http://www.lanczglobal.com/mo/Default.aspx?tabid=88&ctl=Edit&mid=883
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; MDDC; .NET4.0C; .NET CLR 1.1.4322; InfoPath.1; AskTbARS/5.8.0.12304)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 3b8e1395-d3f3-47cb-b306-8ba738995764
InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.UI.Skins.Skin.AddModuleMessage
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.UI.Skins.Skin.AddModuleMessage(Control objControl, String Heading, String Message, ModuleMessageType objModuleMessageType, String IconSrc) at DotNetNuke.UI.Skins.Skin.AddModuleMessage(Control objControl, String Heading, String Message, ModuleMessageType objModuleMessageType) at DotNetNuke.Modules.Html.EditHtml.cmdSave_Click(Object sender, EventArgs e) at System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---


AssemblyVersion: 5.6.1
PortalID: 0
PortalName: LanczGlobal Member's Only
UserID: 1
UserName: host
ActiveTabID: 88
ActiveTabName: ABL Personal
RawURL: /mo/Default.aspx?tabid=88&ctl=Edit&mid=883
AbsoluteURL: /mo/Default.aspx
AbsoluteURLReferrer: http://www.lanczglobal.com/mo/Default.aspx?tabid=88&ctl=Edit&mid=883
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; MDDC; .NET4.0C; .NET CLR 1.1.4322; InfoPath.1; AskTbARS/5.8.0.12304)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: a1fe3165-6b6a-491a-92bd-4f95aa2ecf6f
InnerException: Deleted 0 files, however, some files are locked. Could not delete the following files: C:\inetpub\wwwroot\LanczGlobal\MO\Portals\0\Cache\Pages\1076_ACABA51644A302FBB325E30E7931BAF8.attrib.resources;
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.Services.ModuleCache.FileProvider.Remove
StackTrace:
Message: System.IO.IOException: Deleted 0 files, however, some files are locked. Could not delete the following files: C:\inetpub\wwwroot\LanczGlobal\MO\Portals\0\Cache\Pages\1076_ACABA51644A302FBB325E30E7931BAF8.attrib.resources; at DotNetNuke.Services.ModuleCache.FileProvider.Remove(Int32 tabModuleId) at DotNetNuke.Entities.Modules.ModuleController.SynchronizeModule(Int32 moduleID) at DotNetNuke.Modules.Html.EditHtml.cmdSave_Click(Object sender, EventArgs e)

Hi Sebastian,
What message would the HTML module be trying to display?  I'll check into disabling the antivirus from scanning the temp/cache directories for DNN and .NET framework and report back.

More updates, the pages offending have the Reports 5.0.0 module which originally had caching setup as it was just pulling a flat table that changed maybe once a day from a database. I tried setting the Cache Duration to 0 still got the error. Next I tried changing Output Cache Provider to None as recommended below and saved, but when going back into module settings it is set back to File so it isn't saving that setting. I see that there is a 5.1 version, any idea if this has been fixed in that version?


Cache Settings:
Output Cache Provider: File (Inherited)
Cache Duration (seconds): 0
This module has indicated a recommendation to disable caching (select NONE from the Output Cache Provider list above). Enabling caching on this module is not recommended and may cause the module to display stale data.