External Procedure failes within MTS Transaction

Question

Setup:
Database 9.2 on Win2000Server, Client 9.2 on WinXP
COM+ Component 'XComp' calling a Stored Procedure 'StProc' via ODP (V9.2.0.4).
'StProc' calls an external Procedure void ExtProc(char* pRetString).
The call of ExtProc fails with ORA-03001 (function not implemented) and ORA-06512 (?),
if XComp acts within a MTS transaction.
If XComp has no transaction-context, everything works fine.
Has anyone a hint what I do wrong?
Remarks:
I tried ExtProc as a 'do-nothing' function in a clean win32 dll (no ATL,COM,.NET,...) with the same effect.
I also cleaned the procedure 'StProc'
Procedure StProc IS
ID varchar:='XXXXX';
Begin
ExtProc(ID);
End;
void dllexport ExtProc(char* pRetString)
// strcpy(pRetString,"Test");
}

Answer 1

Certain features are disabled in distributed TXs, especially explicit commits, such as: DBMS_LOCK, autonomous TXs, DDL. Perhaps, external procedures are not allowed since Oracle cannot inspect the code, ie. Oracle cannot check for local commits. Don't know, just guessing.
Armin