When SQL Server is installed (2008 anyway) it creates some local windows groups with names like SQLServerSQLAgentUser$Myserver$MSSQLSERVER and you'll see they have descriptions such as "Members in the group have the required access and privileges to be assigned as the log on account for the associated instance of SQL Server Agent." Log onto the server and look at "local users and groups" to see them.

Your service accounts should each be members of the group for the service they are running. If you've gone for the local system account you'll probably see NT SERVICE\SQL SERVERAGENT in there but if it's a domain account you are using then you may need to add it to the group.

If you have multiple instances of SQL Server on one server you will find a set of groups for each instance or rather for each service - you only get one Integration Services and one Browser service on a server.

This goes a long way to ensure that the account running sql agent has the permissions to access all the disks it needs to read/write.