No, I am able to connect to the sql server with those users.
I have one user who has sysadmin role. I do login to the sqlserver using that user.
I am trying to lock/Unlock other sqlserver users by using sp_grantlogin and sp_denylogin

EXEC sp_denylogin 'work'

but i am getting the following error

'Work' is not a Valid Window NT name. Give the complete name: <domain\username>. Here 'work' is one of the users with sql server authentication.