I ran into this yesterday and wanted to point it out in case you run into the same issue.
When calling a c# dll that has an associated .config file from a VFP executable, you have to name the .config file of the dll to your VFP application exe name.
Fortunately, Rick has this documented here.
http://www.west-wind.com/webconnection/wwClient_docs/_36e0qlogr.htm
"Note that a .config file must be set up for whatever top level EXE file is running the application. This means:"
YourApp.exe.config (your own EXE)
VFP9.exe.config (running VFP IDE)
Thanks Rick!
Craig