authentication error after adding an article

Hi

-- edited 26/02 to clarify the security model --

Using HTTPS merge replication

The subscriber was able to get the snapshot ok, then synchronise fine

However after adding an article to the publication and recreating the snapshot I get this error now at the subscriber

Microsoft.SqlServer.Replication.ComErrorException (0x80004005): A failure occurred when accessing 'usp_misc_dailyTasks_3.sch' due to an operating system error [2='The system cannot find the file specified.'] during Web synchronization. Ensure that the -InternetLogin user when using basic authentication and the user running the merge when using Windows integrated authentication has been granted access to the snapshot share.

at Microsoft.SqlServer.Replication.MergeSynchronizationAgent.Run()

The key properties when synchronising are as follows:
agent.PublisherSecurityMode = SecurityMode.Standard
agent.DistributorSecurityMode = SecurityMode.Standard
agent.InternetSecurityMode = SecurityMode.Standard

In order to create the subscription:

subscription.UseWebSynchronization = True
subscription.InternetUrl = webSyncUrl
subscription.InternetSecurityMode = AuthenticationMethod.BasicAuthentication
subscription.SubscriberType = MergeSubscriberType.Anonymous
subscription.SyncType = SubscriptionSyncType.Automatic

Thanks
Bruce

is it possible that the merge agent was running the same time as the snapshot agent, and that the merge agent was trying to apply a file that was just deleted, but not-yet-created by the snapshot agent?sql