SAP-Adapter Error "The segment or group definition E2IDKU5 was not found in the IDoc metadata."

During runtime, we received the following error from the WCF SAP adapter:

Microsoft.ServiceModel.Channels.Common.XmlReaderGenerationException ist aufgetreten.
  HResult=-2146233087
  Message=The segment or group definition E2IDKU5 was not found in the IDoc metadata. The UniqueId of the IDoc type is: IDOCTYP/3/PEXR2002//701. For Receive operations, the SAP adapter does not support unreleased segments.
  Source=Microsoft.Adapters.SAP
  StackTrace:
       bei Microsoft.Adapters.SAP.TypedIdocBodyWriter.OnWriteBodyContents(XmlDictionaryWriter writer)

The reason was that the IDoc contained the element name E2IDKU5 although its segment definition was E2IDKU5001.

So, whenever you run into a similar message, it's worth to check the SAP transaction WE60 to check the segment definition of the element.
 

How to solve Problems when accessing an IDoc with the SAP Adapter

If you can't see an IDoc when you try to create a schema in Visual Studio using the SAP adapter (building on SAP .net connector 1.0.2), the problem is usually that the IDocs hasn't been published ("freigegeben"). You can check this here:

we60 - Check whether your IDoc is known in a specific SAP Release (we often had the problem that segments of an IDoc weren't known in a release)

we30 - You can check here whether all segements are published. Click on the segment, then "segment editor". There's a checkbox whether this segment is published.

we20 - If you can access the IDoc but can't send data to it, the IDoc might miss a partner agreement ("Partnervereinbarung").