Orphaned transaction (SPID -2) with UOW ID 00000000-0000-0000-0000-000000000000
The KILL command cannot kill a UOW of {00000000-0000-0000-0000-000000000000}, so that leaves you hanging on what to do next to get rid of it.  

To get rid of spid -2 with the unit of work {00000000-0000-0000-0000-000000000000} you can do something, but it has side-effects:

Exec Sp_configure 'in-doubt xact transaction',2
-- This presumes ALL in-doubt trans are aborted
-- so it should be used with great caution.
GO
DBCC dbrecover('dbname'); -- or Alter database


I ran into this problem when test restoring databases.  We had one database that restored successfully, but failed during the DBCC CHECKDB because of a {00000000-0000-0000-0000-000000000000} UOW.

In that case DTC was not running on the restore server at all, but still the 
{00000000-0000-0000-0000-000000000000} UOW was causing us problems as noted above.  So you could say that this was an edge case.

Using the approach above finally cleared the problem for us, but if you use this technique you need to make sure that you are not aborting DTC connections that are in active use.