LanView cashes when running -NET-Dll (System.NullReferenceException)

[OnlyOne]

Hallo,
i have a .net DLLwhich crashes when called in Labview. When i run it in an external exe-file then the DLL works.
Attached a screenshot after the crash.
The DLL calls:
1. COM-Port Open
2. a function with 3 results
3. COM-Port close

The interesting thing is, that "Open" works always, and the crash happens when beginning to execute the "function", but then i see in the foreground the "crash-message" but in the background the VI continues executing and returns the values of the function. Then the "Close" is also executed.

Is there a trick what to do against this crash?
(When i run the DLL in TestStand, then i see the same error message)

Thanks for all tipps

[OnlyOne]

I found out that after the Crash-Message (see attachment "01-labviewcrash.jpg"), that i can move this window to the side and can execute  the VI again. And the VI works again and returns the correct values. So the error cant be so hard i think.

I´m using LV 8.2.1 , see screenshot "02-installedSw.JPG" for the .Net-versions

Is there perhaps a switch somehwere to avoid these messages?