I think I've found out what is happening: after the batch script has entered "admin" and pushed "enter", it appears to push "enter" again and then type the password, whereas what needs to happen is for it to enter "admin", push "enter, enter the password and then push "enter".
This can be seen in this example:
Login: admin
Password: <-- The password needs to be entered here (it is not shown when it is typed, I don't know if that makes any difference?)
**** <-- Not here which is what appears to be happening.
Any ideas?