Few of the fixes for the oracle adapter before attempting to break your head over the errors logged in the eventlog.

FIX: An event may be logged when you use BizTalk Adapter for Oracle Database

http://support.microsoft.com/kb/919607 

 FIX: Error message when you use Microsoft BizTalk Adapter for Oracle Database and when you call a stored procedure on an Oracle server: "Error Code 6550"

http://support.microsoft.com/kb/927607

FIX: BizTalk Adapter for Oracle Database modifies the data in the DateTime field when you use the Insert method, the Update method, or the Query method

http://support.microsoft.com/kb/921999