SQL Server 2008 R2 Replication not working - my 1st try
Your Snapshot Agent process account does not have sufficient permissions to access the snapshot folder.

In the section Permissions That Are Required by Agents in Replication Agent Security Model, the Snapshot Agent process account requires db_owner in the distribution and publication databases and needs read, write, and modify permissions on the snapshot share.

Have a look at Lesson 2: Preparing the Snapshot Folder for more information.