Recently during migration BizTalk project from SQL to WCF adapter had some rather confusing moment. After deploying to test environment WCF ports started generate errors like this:

Failed to open Microsoft.ServiceModel.Channels.Common.Channels.AdapterRequestChannel, Faulted Microsoft.ServiceModel.Channels.Common.Channels.AdapterRequestChannel, Faulted System.ServiceModel.Channels.ServiceChannel, Failed to open System.ServiceModel.Channels.ServiceChannel

 After few frustrating troubleshooting sessions it was found that adapter binding was missing identifier for the default database instance. Here's what we had:

Both adapters worked in development, but in test WCF did not. What was missing is "//" between server and database part of the URI. This is not required for SQL adapter configuration but apparently is critical for the WCF adapter. So the correct URI should have been: mssql://TestServer//Database.

Read the complete post at http://geekswithblogs.net/paulp/archive/2009/07/02/133222.aspx