Client/Server App won't launch on Windows 10 (Event 1026).


Apr 10, 2006
Toronto Canada
Programming Experience
I hope someone out there can help me.

I have a big client/server app written with VS 2010 and it won't launch on
Windows 10. This app is running on my Win 7 and client's Win 7 PCs since 2014
but it is time to upgrade and I get this problem after I installed it on a
Win 10 PC and launch it.

Behaviour: After clicking the app, I see the time icon flash twice in quick
successions for a fraction of a second. This is a big app and it normally
take over a minute to launch on Win 7.

Event Viewer Shows: Event ID 1026 followed by 1000.
The details of Event ID 1026 shows:
1) Unhandled Exception: "System.IO.FileNotFoundException at"
AppName.frmCustomer.ctor() at
and a few other forms "at" ...
2) System.TypeInitializationException at AppName.SubMain.Main()
SubMain is the entry point for this app.

So far I have tried the following on the Win 10 PC:
1) Create the folder "URTInstallPath_GAC" inside the "Microsoft.NET\Framework"
and on the Framework64 folders (As someone has suggested).
2) Changed the property of the exe's compatibility to run under Win 7
(also as someone has suggested).
3) Verified the framework as V4.0.30319. It is installed.

On the project, I changed the app.manifest compatibility section to
activate "supportedOS ID" to work with Win 7.

I also verified the Setup project and it should run on "Any CPU"

Nothing works.

I know it is in the process of loading the app as opposed to executing it
because it normally takes a long time to launch it, definitely not
a second or 2.

Features of this app that might be relevant:
1) This app was originally written for VS 2002, and it was changed to
run on VS 2005. These versions worked on Win XP.
2) From VS 2005, it was re-created as a VS 2010 project. This was not an
upgrade but a re-build. I.e re-creating the GUI then cutting,
pasting and massaging the code. This version was implemented on
2014 on Win 7 machines. It has been working since then.
3) It extracts values from "app.config"
4) It has access to MS SQL Server 2008 R2 on my local Win 7 machine and on a
Windows 2011 SBS Server.
5) It uses CrystalReports and has tens of these.
6) It has 40 forms.
7) Some forms uses Text Files with System.IO.
8) The frameworks installed on the Win 10 machine are:
v1.0.3705 V1.1.4322 V2.0.50727 V3.0 V3.5 V4.0.30319

I followed some threads on social media but could not find anything
helpful. Maybe it is a framework problem or something else.

Please help. I am baffled.
Last edited:
1) Unhandled Exception: "System.IO.FileNotFoundException at"
AppName.frmCustomer.ctor() at
and a few other forms "at" ...
That is telling you what the problem is and where. It is unable to find a file that it is looking for in the constructor of frmCustomer.
The app won't even launch.

The job of the CLR is to load the app as per manifest, launch it, then
transfer control to it, is it not?. In this case, it hasn't completed
loading it. It is not the CLR's job to second guess what the app may or
may not do. That is up to the app at runtime.

The particular form (frmCustomer) you mentioned DOES NOT access any
file. None of the other forms listed does. What the app and this form does
is access a database which could be in the local machine or remotely in a
Windows 2011 server. Which server the database is in will be selected by
the user during their sign-in process. Since nothing shows-up, the user
cannot sign-in nor select a server.

The only thing that remotely resembles accessing a file is "SubMain".
It extracts values from "app.config" but this is component of the app and
it is never opened or read through "System.IO". It is just there as it
was forever.

The question really is: Why this app runs smoothly on all Win 7 PCs
where it is installed (there are over 10 of those since 2014)
but not on a WIN 10 machine? Previous Versions of this app developed in
older VS versions (2002 & 2005) worked on Win XP without problems.

My client's machines are getting old and need to be replaced.
This app is critical to their business operation and has to work
in Win 10.

Win 10 wants something, What is it?