CONTEXT
https://sites.google.com/site/easylinuxtipsproject/2
'But in "Users and Groups" the new username should begin with a capital letter, because otherwise a malfunction might occur.'
PROBLEM
After 'Add' button in 'Users and Groups' window, the pop-up window carries the message 'The username must consist of only: -lower case letter (a-z) ...' and will not activate the 'Add' button unless the 'Username' field contains no capital letters.
CONSEQUENCE
Therefore a skeleton for guest cannot be created according to the 'Hospitality' instructions.
HOST
Kernel: 3.16.0-46-generic x86_64 (64 bit, gcc: 4.8.2)
Desktop: Cinnamon 2.6.13 Distro: Linux Mint 17.2 Rafaela
This system is a clean install with modifications only according to your site.
REQUEST
Please advise fix.