I'm posting this in case someone else gets this problem... I've solved it, but it took a few days of head-scratching when it shouldn't

All staff were forced to change their passwords in week 2 of this term and our Year 6 teacher has been complaining that since she did it, she couldn't login in our IT suite, but could elsewhere. A large part of me was thinking PICNIC (problem in chair not in computer), but then I had a eureka moment yesterday!

The IT Suite was installed by someone else and before anyone else logs in... the keyboard mapping is US, not UK. The teacher had recent her password to something more complex and the characters she typed weren't what she thought she was getting from the keyboard

She's reset her password to something more simple and I have 18 PCs to adjust!