Ok, so it is session 507 which has had an active transaction since the 5th of April (last week friday)
You may want to do some investigation as to how and why the session has an open transaction that long, so that you can ensure it doesn't happen again, then kill it.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability