A payroll backup can fail if there are permission restrictions on the destination where the backup is being saved. To fix this, make sure this location or folder is not set to read only and that you have full control access. If you're not sure how to do this, you might need help from an IT person.
Alternatively, you can change the backup destination to a folder where you have full access, for example the Documents folder or your Desktop.
The payroll backup can also fail if MYOB Payroll can't write to the file path selected. For example, if you're saving to a USB stick and the USB is not plugged in or is corrupt.