ReplMerge works on one machine

I have a user who does not have the subscription listed in Sync Center so I have prepared a batch file to run replmerge

This runs fine on an XP machine
but errors : 'another merge agent for the subscription or subscriptions is running or the server is working on a previous request by the same agent'
for a win 7 machine

all I do is change the Subscriber
The Prublisher and Distributor both need SQl authentication

anyone have any ideas where I should be looking? what sort of things could cause this problem?

Thanks in advance

jnc