ODBC error strings are returned in two parts. The first part is the generic  "ODBC 
call failed"  error message; the second part is the specific error message. If you use 
the Err() function to trap only the error number (which is  3146  for a duplicate 
unique index), you trap only the first part, the generic  "ODBC call failed"  error 
message. To get the specific error message, you must parse the full error string 
that is returned. 
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This article describes how to get more information on the ODBC Call Failed error. 
When errors occur using ODBC databases, Visual Basic will provide an  "ODBC Call 
Failed"  error message. This generic error message provides no specific detail so you 
must cycle through the Errors collection to get additional information. Below is a 
code sample that shows the difference in behavior.

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' DAO Error Handler
      Dim MyError As Error
      MsgBox Errors.Count
      For Each MyError In DBEngine.Errors
        With MyError
          MsgBox .Number & " " & .Description
        End With
      Next MyError

      ' RDO Error Handler
      Dim MyError As rdoError
      MsgBox rdoErrors.Count
      For Each MyError In rdoEngine.rdoErrors
        With MyError
          MsgBox .Number &  " "  & .Description
        End With
      Next MyError