replication issues between seperate servers

I have following scenario:

1- publisher / distributer running on one named instance \\MACHINENAME\SQLMASTER

2- subscriber running merge subscription on  another named instance \\MACHINENAME\SQLSLAVE .

if I run both these instances on same server and choose the following options for agents

"Run under the SQL server agent service account"    &

"connect to publisher :  by impersonating the process account" 

it all works fine BUT  if i move the subscriber instance to a seperate box it does not work .. 

i am still not clearly understanding the usage of the indivisual accounts in my scenario I think.

Sami