I kept having the Resgen.exe error as well. I followed the directions on the Open Dental Source Code page;
http://www.opendental.com/manual/sourcecode.html
After Line 3 I had a problem:
3. Copy and paste:
Corflags /32Bit+ /Force ResGen.exe
then Enter. If successful, you will see about 5 lines of text, including "warning CF011: The specified file is strong name signed".
Instead I received the response; "Corflags is not recognized as an internal or external command"
So I researched Corflags and it brought me to the MSDN site where it says;
Where to get corflags.exe. It comes as part of Visual Studio 2010. Open up a "Visual Studio Command Prompt" (not a normal command prompt, as the path won't be set up), and you can call it.
I am currently using C# Express. So my assumption is that the express version will not compile Open Dental and the full version of Visual Studio is required.