Your code is running fine i have checked in SQL 2008 as below

DECLARE @killspid int , @CMD nvarchar (20)

DECLARE cur_kill CURSOR FOR SELECT SP.spid, SD.name

FROM SYSPROCESSES...

Please check browser port is 1434 is open or not

run below command

telnet servername 1434

if this is not open you have to add in coonection string

instancename,tcpip port

if this is running...

This type of error 'NULL' comes when the service accounts is not added in windows acivie dictonary on Production server.

Because the agent could not able to contect at the production...