.NET Questions and Solutions

Symptoms
When you use the IList interface with a Visual Basic .NET collection object in Visual Basic .NET (2002) before you use the Insert property, you can insert elements in the list at index -1. If you insert an element at index -1, you receive the following error message when you try to read the element by using the Item property at index -1:

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Resolution
The IList index has a base of -1 instead of zero. Therefore, you can insert an element at index -1 even though MSDN documentation states that the IList index is zero-based. However, you receive an error when you try to read the value from the IList at index -1.

Symptoms
When you try to add a project reference to a Component Object Model (COM) DLL in Microsoft Visual Studio .NET, you may receive an error message that is similar to the following:

A reference to ‘C:\MyCOMDLL\Debug\MyCOMDLL.dll’ could not be added. Converting the type library to a .NET assembly failed. Could not load type MyCOMDLLLib.MyClassClass from assembly Interop.MyCOMDLLLib, Version=1.0.0.0.
Additionally, when you try to convert the type definitions that are found in a COM DLL by using Microsoft Type Library Importer (Tlbimp.exe) from a command prompt, you may receive an error message that is similar to the following:

TlbImp error: System.TypeLoadException – Could not load type MyCOMDLLLib.MyClassClass from assembly MyCOMDLLLib, Version=1.0.0.0.
Resolution
You may notice the behavior that is mentioned in the “Symptoms” section when the following conditions are true: Your DLL contains a class (such as MyClass) that implements an interface (such as IMyClass) that in turn derives from a base interface (such asIBaseClass).The IMyClass interface contains a method (such as Test) that has the same name as a property that the IBaseClass interface has.You notice this behavior because of the mechanism that Tlbimp.exe uses to disambiguate member names. Under the previous conditions, when the Microsoft .NET Framework tries to create a method implementation to associate the Test method of the MyClass class with the corresponding interface method, the .NET Framework does not know the name of the corresponding interface method. Therefore, Tlbimp.exe generates a System.TypeLoadException error, and then you receive the error message that is mentioned in the “Symptoms” section.
When you try to add a project reference to a COM DLL, Visual Studio .NET internally runs Tlbimp.exe and then handles any generated exceptions. Therefore, under the previous conditions, Visual Studio .NET handles the generated System.TypeLoadException, and then you receive the error message that is mentioned in the “Symptoms” section.