Deploying an ASP.NET JSON-RPC web service on IIS 7

I've got an ASP.NET JSON-RPC web service which work well using the Visual Studio development web server. It has three dependencies: Jayrock, Log4net and a COM DLL (AcoSDK) to be able to access a C++ application.

I'm trying to deploy it on IIS7 in a SBS 2008 server, but I'm having lots of troubles. The application files are in "C:\intepub\wwwroot\AcombaConnect_Deploy" include the bin folder with the compiled binaries. The folder has been converted to an application, but the application would not start so I had to add the following section to the Web.config file:

<system.webServer>
  <handlers>
    <add name="AcombaConnect.Acomba" verb="*" path="*" scriptProcessor="C:\\Windows\\Microsoft.NET\\Framework\\v4.0.30319\\aspnet_isapi.dll" type="AcombaConnect.Acomba, AcombaConnect" resourceType="Unspecified"/>
  </handlers>
  <directoryBrowse enabled="false"/>
</system.webServer>

At that point the app was throwing: "bad module "ManagedPipelineHandler" in its module list" and I've tried everything from https://stackoverflow.com/questions/8659862 to no avail. I then tried to switch the application pool to the integrated one and added the following to the Web.config file:

<system.webServer>
  <validation validateIntegratedModeConfiguration="false"/>
  ...

Now, it seems the application is starting, but I only get "HTTP Error 503. The service is unavailable."

Does anybody know where to go from there?

P.S.: I don't have much experience with IIS7. I'm not sure where to look for more detailed error messages.