Calling A Sub Trans Within An SQL Trans Block

In an MII transaction (V15), from within an SQL Transaction block (after the Begin and before the End), I am trying to call another transaction and I am getting this error:

Error found trying to execute action ... unable to create transaction instance

Are you not able to call a transaction from within an SQL Transaction block?  I can call the same transaction if it is outside the SQL Transaction block.

Thank you,

Mike