Finding the lead blocker in a chain of blocks is a difficult challenge when using sp_who2. There are also a lot of detect blocking scripts that I have run in production environments that seem to block things themselves.
Probably the most efficient way to detect blocks is to query sysprocesses. The following script displays the lead blocker in a chain of blocks:
SELECT spid ,status ,loginame = SUBSTRING(loginame, 1, 12) ,hostname = SUBSTRING(hostname, 1, 12) ,blk = CONVERT(char(3), blocked) ,open_tran ,dbname = SUBSTRING(DB_NAME(dbid),1,10) ,cmd ,waittype ,waittime ,last_batch FROM master.dbo.sysprocesses WHERE spid IN (SELECT blocked FROM master.dbo.sysprocesses) AND blocked = 0
