32/64-bit Installation of Oracle Adapter

After installing the Oracle Adapter, it might be that you run into errors in run-time, though you solved all the problems so that you could connect to Oracle in VS. ;-) I ran into the following error
System.IO.FileNotFoundException: Die Datei oder Assembly Oracle.DataAccess, Version=2.111.7.20, ...

Actually, the Oracle WCF adapter found the assembly 2.111.7.0, but was searching the Oracle.DataAccess.dll in the BizTalk installation folder:

LOG: Diese Bindung startet im default-Load-Kontext.
LOG: Die Anwendungskonfigurationsdatei wird verwendet: D:\Program Files (x86)\Microsoft BizTalk Server 2009\BTSNTSvc64.exe.Config
LOG: Die Computerkonfigurationsdatei von C:\WINDOWS\Microsoft.NET\Framework64\v2.0.50727\config\machine.config wird verwendet.
LOG: In der Anwendungskonfigurationsdatei wurde eine Umleitung gefunden. 2.111.7.0 wird nach 2.111.7.20 umgeleitet.
LOG: Verweis nach der Richtlinie: Oracle.DataAccess, Version=2.111.7.20, Culture=neutral, PublicKeyToken=89b483f429c47342
LOG: Download von neuem URL file:///D:/Program Files (x86)/Microsoft BizTalk Server 2009/Oracle.DataAccess.DLL.

The problem was inconsistent image-typing: While VS ran in 32bit, the BizTalk host instance ran in 64bit so that it didn't look in the GAC... Using a 32-bit host instance solved the problem; however, more elegant might be to install a 64-bit version of the Oracle.DataAccess (that however could cause problems with a 32-bit VS...)

Furthermore, deploy the policies "policy.2.x.Oracle.DataAccess" into the 32- and the 64-bit GAC to because both VS and the administration console of the BizTalk are searching for the assembly.