This is a common error that you would have faced, while adding a WCF service endpoint to BCS through SharePoint Designer 2013, connected to Office 365. The complete error would look like this:
Unknown Error occurred. Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.
This is an error observed while connecting to a WCF data source through SharePoint Design 2013. Ensure that your WCF service endpoint is working perfectly.
STEP 1: Open the “SPDESIGN.exe.config” file from SharePoint Designer folder ()
STEP 2: Update the file with the following configuration:
<?xml version=”1.0″ ?>
<requiredRuntime version=”v2.0.50727″ />
<supportedRuntime version=”v2.0.50727″ />
<assemblyIdentity name=”Microsoft.BusinessData” publicKeyToken=”71e9bce111e9429c” culture=”neutral” />
<bindingRedirect oldVersion=”18.104.22.168-65535.65535.65535.65535″ newVersion=”22.214.171.124″/>
STEP 3: Save the file and run SharePoint Designer once again.
STEP 4: Try adding your WCF data source once again. Voila! you should see it work now…:)
The fix is just telling SPD to run BCS on version 126.96.36.199, if its gets a reference to version 188.8.131.52. I guess our Office 365 online considers SharePoint 2013 version as 16, instead of 15. Forward thinking…quite understandable…:)
Hope this helps!