If Cashbook is asking for a login user name and password, it is because Cashbook has been set to Multi-User. Once this is done, each person requiring access to Cashbook will have to supply a username and password.
To revert back to single-user mode
Log in using a username = 'administrator' and password = 'Admin'
Click on the File/Multi-User - click to disable menu option
iii. This will then prompt that Cashbook will be closed