Generally, you should avoid using mapped drives. The main reason is that mapped drive names can change easily and is not shared across users the same way.
The best approach is to use UNC paths only, together with a Credential.
If you really need to map a drive you should not use a Credential together with the mapped drive as it already is using a Credential when the drive was mapped.
If you have problems mapping a drive you could try the following:
1. change the user that runs the VisualCron service to a domain user, then try to map - without a credential
2. if that does not work then try 1. and map with a Credential