The TxScopeTransactionManager class don't overrides the DoSetRollbackOnly (from AbstractPlatformTransactionManager), which throws exceptions on nested transactions;
throw new IllegalTransactionStateException(
"Participating in existing transactions is not supported - when 'IsExistingTransaction' " +
"returns true, appropriate 'DoSetRollbackOnly' behavior must be provided");
I checked out the HEAD of spring.net and the problem still happens there....