I was looking for a Grid ActiveX control similar to MsFlxGrid as the MsFlxGrid is not available for 64-bit MFC application. Please let me know if the latest IGrid control (version 6.5) is 64-bit compatible?
We can't provide true 64-bit version of iGrid ActiveX for historical reasons. iGrid ActiveX is developed in Visual Basic 6. This development environment produces only 32-bit executable files. We have been trying to find a way to recompile code for 64-bit environments for years but no luck yet. See, for instance, my post  on StackOverflow.

The only hope for a solution to this problem is the RAD Basic  project. We are in contact with Carles Royan, the main developer of RAD Basic, and are waiting for the moment when this development environment can compile existing VB6 ActiveX projects to native 64-bit executable code. If this ever happens and we can recompile our iGrid ActiveX for 64 bits, we will update this thread. At the moment, everybody can support this project at Kickstarter: 
Absence of 64-bit versions of many ActiveX controls and libraries is a serious problem for all developers writing apps for Microsoft Office. If you are heavily using other 3rd-party components, in many cases you have no option except using the 32-bit Office. Even Microsoft recommends using the 32-bit editions of Office if you are developing Office apps on the VBA platform, including the case of using ActiveX controls:

Choose between the 64-bit or 32-bit version of Office 

If you need to build a solution for a 64-bit edition of Microsoft Office, consider our iGrid for .NET. We even published an article demonstrating how to start to use iGrid.NET in Microsoft Office with VSTO (Visual Studio Tools for Office). We are building an Excel add-in that displays a form with iGrid in this article:

Basic Example of Excel VSTO Add-in: Display Form with Grid