Settings -> backup & reset ->factory data reset, asking for password which was never set

[avi_p]

Settings ->  backup & reset ->factory data reset, asking for password which was never set. Please anybody would help?

I tried last four didgits of my mobile number, which did't work.

[Alijanjan]

Worked for me, Thanks a lor

[chevalier]

0000 does not work

my old screen lock password does not work

I was not prompted to set a password.

Help!