I have a WCF service from which I want to return a DataTable. I know that this is often a highly-debated topic, as far as whether or not returning DataTables is a good pract
The best way to diagnose these kinds of WCF errors (the ones that really don't tell you much) is to enable tracing. In your web.config file, add the following:
You can then open the resulting file in the SvcTraceViewer.exe utility which comes in the .NET Framework SDK (or with Visual Studio). On my machine, it can be found at %PROGRAMFILES%\Microsoft SDKs\Windows\v6.0A\Bin\SvcTraceViewer.exe.
Just look for an error message (in bold red) and that will tell you specifically what your problem is.