VFS Not able to make an appointment(Login failed for VAF UserId)

I assisted my sister, uncle and dad to apply for the LEP in February this year online using the same link, made payments which are reflecting when i go onto their website. When i try to schedule an appointment, I get an error login failed for VAF userid. After long struggle of visiting the PE branch my uncle eventually got sorted and my sister not. My dad went to George branch and got assisted. My sister still struggling and now needs to reapply and pay again. No one can give answers as to why they are able to get the other 2 applications and not hers. Mind you she app**** the same time with my uncle.