So did you try some of the things I had suggested?
Also, why is AutoCAD on your E: drive? I am assuming that Windows is on your C: drive, you may be having a problem of .NET and/or AutoCAD can't 'see' each other. On my PC I have an entry in the path of 'c:\program files\common files\autodesk shared\;'. You could also try and install AutoCAD on your C: drive.
Hmmm......also, try to remove all references to AutoCAD: Interop, Managed, etc and re-add them.
And finally, are you able to run and/or debug AutoCADs examples? Are you having the same problem with those as well? You really need to try and run those to see if they work. Granted, most of them don't add command buttons, but you can netload and type in the command names to see if you can run/debug.
Samples and Documentation:
1). First I built your sample which worked great. So I tried to make a project of my own from zero. Of course it didn't work; I copied all your classes still didn't work. Hmm ... I tried the project settings, they were the same, so that wasn't the problem., but something was still wrong.
So, I thought about the DLLs. I removed and added the DLL's for AutoCAD: acdbmgd, acmgd, Autodesk.AutoCAD.Interop and Autodesk.AutoCAD.Interop.Common and set their "Copy Local" property to false. Now it WORKED.
I tried to figure out why the commands did not work if the AutoCAD DLL's where local copied, but I didn't have any success. What I realized is that not all the dll's are the problem, but only the "acmgd.dll" which must not be local copied.
If you know why, please explain me cause I'm very curious.
2). What is the problem with debugging I don't really understand. For me it works fine. I run the solution in debug mode and set some breakpoints. In AutoCAD I netload my dll and my breakpoints fire. So, it's okay for me.
3). Why shouldn't I put my plugin dlls in the ..\Program Files\AutoCAD 2007\ .. directory?
I ran into the same problem. Thefix taht worked for me was to set the startup directory for debugging to your AutoCAD folder and then set AutoCAD as your start up application. Should fix it for future people that come across this post.