This is an orphaned DTC transaction. Unfortunately it still holds locks and causes blocking. The fallowing URL contains explanations and the way to kill this process http://www.sqlserverclub.com/articles/how-to-deal-with-negative-spids-in-sql-server.aspx
Adi
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To know how to ask questions and increase the chances of getting asnwers:
http://www.sqlservercentral.com/articles/Best+Practices/61537/
For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/