BUG: Various errors may occur when you try to call managed code from unmanaged code in Visual C++ .NET 2003 (837318)

The information in this article applies to:

Microsoft Visual C++ .NET (2003)
Microsoft .NET Framework 1.1

SYMPTOMS

You have a Microsoft Visual C++ .NET 2003 application that uses multiple application domains. When you try to call managed code from unmanaged code in a DLL that has already been loaded in another application domain, you may receive the following error message:

An unhandled exception of type 'System.NullReferenceException' occurred in mscorlib.dll
Additional information: Object reference not set to an instance of an object.

Note In some scenarios, you may receive one of the following error messages:

DllNotFoundException

Illegal Instruction

CAUSE

You may notice this problem if your application contains unmanaged code and uses multiple application domains.

For example, if you have an application that uses multiple application domains that use a set of DLLs, you can successfully load and use these DLLs in the first application domain. However, when you try to call the managed code in one of these DLLs from unmanaged code in a different (second) application domain, the behavior that is mentioned in the "Symptoms" section of this article occurs. The application does not load the managed code in the second application domain because the code has already been loaded in another application domain that is in the same process.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section of this article.

REFERENCES

For more information, visit the following Microsoft Developer Network (MSDN) Web sites:

Managed Extensions for C++ programming
http://msdn.microsoft.com/library/en-us/vcmex/html/vcconMCOverview.asp

Application domains
http://msdn.microsoft.com/library/en-us/cpguide/html/cpconApplicationDomains.asp

AppDomain class
http://msdn.microsoft.com/library/en-us/cpref/html/frlrfSystemAppDomainClassTopic.asp

NullReferenceException class
http://msdn.microsoft.com/library/en-us/cpref/html/frlrfsystemnullreferenceexceptionclasstopic.asp

Modification Type:	Minor	Last Reviewed:	12/30/2005
Keywords:	kbManaged kbDLL kbProgramming kbinterop kberrmsg kbbug KB837318 kbAudDeveloper