distributed transaction

Hi All,
I am trying to use distributed transaction (using linked Server).
But getting the folloing error..

Some one please help...

following is the error...

The operation could not be performed because the OLE DB provider 'MSDASQL' was unable to begin a distributed transaction.

[OLE/DB provider returned message: [Microsoft][ODBC SQL Server Driver][SQL Server]Transaction context in use by another session.]
OLE DB error trace [OLE/DB Provider 'MSDASQL' ITransactionJoin::JoinTransaction returned 0x8004d00a].The first part of your error can occur when your SQL server and your linked server data source reside on the same machine. Is this the case?

The other thing that I would check is wether the MSDTC has been started in your servers services.