It's a permissions issue. You need to check in Headers=>manager.conf that you have a FOP entry. It should look something like this...
[fop]
secret=asterisk
deny=0.0.0.0/0.0.0.0
permit=127.0.0.1/255.255.255.0
read=system,call,log,verbose,command,agent,user
write=system,call,log,verbose,command,agent,user
This example will allow you to run the FOP but ONLY from the same subnet as the SARK box. If you want access from some other subnet then you will have to explicitly permit it with another permit statement.
Kind Regards
S