Installed the DNN 5.4.3. on a couple of test sites - all OK.  Upgraded a production site and received the following error:

[ThreadAbortException: Thread was being aborted.] 
System.Threading.Monitor.Enter(Object obj) +0 
System.Web.HttpApplicationFactory.EnsureAppStartCalled(HttpContext context) +61 
System.Web.HttpApplicationFactory.GetApplicationInstance(HttpContext context) +92 
System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr) +289 

Has anyone else experienced this error?  Any ideas on how it can be fixed?

When did this error occur
The error came during the standard upgrade process.  I have previously tested the upgrade on a couple of other minor sites and all was OK.  I have subsequently tested it on a couple of other sites and it is OK.  Confusing.

Have you restarted the app through IIS?
Yes.   I tried browsing the default.aspx file through IIS (7) with the same result.

What version of DNN did you upgrade from?
Upgrade from 5.4.2 to 5.4.3.  It was a clean 5.4.2 installation (no upgrades from previous DNN versions).

What third party modules are you running?
Here is the list:

MODULE	VERSION	IN USE	MANUFACTURER
Authentication	1.0.0	No
BannerAdvertisers	5.1.7	Yes	Smoke Ranch
BannerDisplay	5.1.4	Yes	Smoke Ranch
Banners	1.0.0	No
Child Links	1.5.1	Yes	Ventrian
CISS.FlashPlayers	2.7.18	Yes	DNN360
CISS.PagePeel	1.0.1	No	DNN361
CISS.SideMenu	1.4.10	No	DNN362
CISS.TuneUp	1.2.4	No	DNN363
Console	1.0.0	Yes
ContentList	1.0.0	Yes
Dashboard	1.0.0	Yes
Dynamic Forms	3.30.61	Yes	Data Springs
Dynamic Login	3.30.2	Yes	Data Springs
Events	5.0.3	No
Extensions	1.0.0	Yes
Feed Explorer	1.0.0	No
Feedback	4.4.3	No
File Manager	1.0.0	Yes
Google Analytics	1.0.0	Yes
Host Settings	1.0.0	Yes
HTML	5.2.0	Yes
IFrame	4.3.0	No
Interactive User Import	2.10.0	Yes
Languages	1.0.0	Yes
Lists	1.0.0	Yes
Log Viewer	1.0.0	Yes
Map	1.0.9	No
Marketplace	1.0.0	Yes
Messaging	1.1.0	Yes
News Feeds (RSS)	4.0.1	Yes
Newsletters	1.0.0	Yes
OnyakTech.Ads	3.0.55	Yes	OnyakTech
PackFlash_PublishDashboard	2.5.1	Yes	PackFlash
PackFlash_PublishDetails	2.5.1	Yes	PackFlash
PackFlash_PublishDisplayIssue	2.5.1	No	PackFlash
PackFlash_PublishIssueTeaser	2.5.1	Yes	PackFlash
PackFlash_PublishList	2.5.1	Yes	PackFlash
PackFlash_PublishRelatedContent	2.5.1	No	PackFlash
PackFlash_PublishRSS	2.5.1	No	PackFlash
PackFlash_PublishSearch	2.5.1	No	PackFlash
PackFlash_PublishSearchResults	2.5.1	No
Portals	1.0.0	Yes
Property Agent	1.7.72	Yes	Ventrian
Property Agent Latest	1.7.72	Yes	Ventrian
Property Agent Search	1.7.72	Yes	Ventrian
Property Agent Types	1.7.72	Yes	Ventrian
Recycle Bin	1.0.0	Yes
Scheduler	1.0.0	Yes
Search Admin	1.0.0	Yes
Search Input	1.0.0	No
Search Results	1.0.0	Yes
Simple Gallery	2.4.18	No	Ventrian
Simple Gallery Latest	2.4.18	No	Ventrian
Simple Gallery Search	2.4.18	No	Ventrian
Simple Gallery Tag Cloud	2.4.18	No	Ventrian
Site Log	1.0.0	Yes
Site Wizard	1.0.0	Yes
Sitemap	1.0.0	Yes
Skin Designer	1.0.0	Yes
Skins	1.0.0	Yes
Solutions	1.0.0	No
SQL	1.0.0	Yes
Subscription Content	1.4.5	No
Subscription Signup	1.4.5	No
Tabs	1.0.0	Yes
Taxonomy Manager	1.1.0	Yes
Users and Roles	1.0.0	Yes
Vendors	1.0.0	Yes
ViewProfile	1.0.0	Yes
Whats New	1.0.0	Yes
Wiki	4.2.0	No

The upgrade to 5.4.3 is now working. Not sure why. * Copied files and database to a new server and it upgraded without error. * Tried the installation on to my localhost - upgraded with no errors. * Then tried the upgrade again on the original server. There was an unspecified error (the custom error message) on my remote browser, but when I browsed from within the server itself I found it had actually upgraded correctly this time with the Host Settings Page reporting version 5.4.3. Browsing from an external computer then worked also. No sign of the previous error messages! * Looking back on the logs for the previous upgrade attempt, there were a series of exceptions on the site at or during the initial upgrade (see below). I am not sure if these are relevant or significant. If I encounter any similar problems upgrading other sites I'll log them. Appologies if this were a one off random error. The rest of my upgrades were impressively uneventful. I look forward to the increased functionality & stability. Cheers - Peter __________________________________________________________________________ AssemblyVersion: 5.4.2 PortalID: -1 PortalName: UserID: -1 UserName: ActiveTabID: -1 ActiveTabName: RawURL: AbsoluteURL: AbsoluteURLReferrer: UserAgent: DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider ExceptionGUID: 471a1e88-655e-4684-92e1-2db654ccdc95 InnerException: This operation returned because the timeout period expired. (Exception from HRESULT: 0x800705B4) FileName: FileLineNumber: 0 FileColumnNumber: 0 Method: System.Threading.ReaderWriterLock.AcquireWriterLockInternal StackTrace: Message: System.ApplicationException: This operation returned because the timeout period expired. (Exception from HRESULT: 0x800705B4) at System.Threading.ReaderWriterLock.AcquireWriterLockInternal(Int32 millisecondsTimeout) at DotNetNuke.Services.Scheduling.DNNScheduling.Scheduler.CoreScheduler.AddToScheduleQueue(ScheduleHistoryItem objScheduleHistoryItem) Source: Server Name: CT105