Hi rphillips,
Welcome to Visual WebGui
It is not easy to say what might be wrong, but the most common cause is some unhandled exception that would prevent your form from loading correctly. I suggest you take a look at the most major breaking changes between version 6.3 and 6.4 which you can see in this wiki article here.
To catch the unhandled exceptions, you might want to open your project in VS2008, Go to the Debug window and select Exceptions (or press Ctrl-Alt-E). In the dialog, you should check the Common Language Runtime Exceptions''s Thrown checkbox, then build your project and run in debug mode (F5) within Visual Studio and see if you catch any errors that way. If you do, they will help you track down the problem.
If you don't get any errors and your form still doesn't load correctly, there's often not much else to do but start removing parts of your form until you get it to run, and then go back step by step until you locate the error.
If this is just a simple application, we might also be able to help you with a quick check, if you would email it to support, but you should first try what I mentioned above.
Hope this helps,
Palli