VB Migration Partner

KNOWLEDGE BASE - Classes and COM objects

Previous | Index | Next 

[PRB] .NET 4.0 TlbImp tool generates wrong wrappers for optional Boolean parameters

Assume that the VB6 project being migrated references a COM DLL or type library that exposes the following function:

    Public Function DoSomething(Optional ByVal boolValue As Boolean = False) As Integer

When migrating on a computer that only has Visual Studio 2005 and 2008 all works well. However, when running on a computer that only has Visual Studio 2010 a problem occurs, because the .NET TlbImp tool that comes with .NET 4 mistakenly converts the function as follows:

    Public Function DoSomething(Optional ByVal boolValue As Boolean = True) As Integer

This bug is documented in this article, which explains that the bug has been solved in Visual Studio 2011.

The only solution for this problem is installing the TlbImp tool that comes with a previous version of .NET, and then forcing VB Migration Partner to use that version.

Previous | Index | Next 

Follow Francesco Balena on VB6 migration’s group on


Read Microsoft Corp’s official case study of a VB6 conversion using VB Migration Partner.

Code Architects and its partners offers remote and onsite migration services.

More details

Subscribe to our free newsletter for useful VB6 migration tips and techniques.


To learn more about your VB6 applications, run VB6 Analyzer on your source code and send us the generated text file. You will receive a detailed report about your VB6 applications and how VB Migration Partner can help you to quickly and effectively migrate it to .NET.

Get free advice

A fully-working, time-limited Trial Edition of VB Migration Partner allows you to test it against your actual code

Get the Trial

The price of VB Migration Partner depends on the size of the VB6 application, the type of license, and other factors

Request a quote

Migrating a VB6 application in 10 easy steps

Comparing VB Migration Partner with Upgrade Wizard

Migration tools: Feature Comparison Table

All whitepapers