Windows 10 x64. Visual Studio 2019 Enterprise.
Create a new project from a template C # Windows Forms App (.NET Framework).
Without changing anything, just run in debug mode.
the main form window opens and then closes.
In non-debug all right – a window opens and remains open as long as it will not close.
What could be the reason?
Thanks in advance.

Answer 1, Authority 100%

RESOLVED.
Many thanks to all responded, especially cProject .

Solver:
In the event logs Windows logs / Applications in the records of the error
name the offending applications: MyForm.exe
The name of the failed module: clr.dll
The way the failed module: C: \ Windows \ Microsoft.NET \ Framework64 \ v4.0.30319 \ clr.dll
Dll-ka in fact normal. What she does not like?

In the event logs Windows Logs / System of
error records
permission settings for a particular application does not give permission for the application running in the container.
Security policy change has not yet want to, but worried by the fact that the system tries to place the container in the debugged application (as insecure), and this feature Comodo. Why is this happening even when the antivirus?

Going into VS. In the project properties (Debug tab) put a tick Enable native code debugging and run debugging again (antivirus is turned off). I get debug message that causes Access violation cmdvrt32.dll. It Comodo library. In the list of running processes can see that despite the fact that the anti-virus not only off, but made out of the program, it is still there
processes from Comodo. Still, anti-virus!

Solution:
The first thing that suggests itself – Comodo and carry put another antivirus. But I decided to do otherwise. In Comodo / Advanced Settings / Containment / Auto-Containment added a rule to ignore Visual Studio. Error disappeared.
Profit!