I'm having problems with sharepoint and if anyone could give me any help that would be great

i'm having an issue with mysites the mysites are created however im having certin issues

we have a root site e.g https://abc.sch.uk/ << this is where departments go to when they need to order stuff

main site https://abc.sch.uk/mainsite << this is where all staff / pupils / parents go

when i login as a pupil / parent / staff under the mainsite everything is fine. but when i click on the pupils mysite link it gives me and access denied error message. however when i look at the link in the url it is pointing to the root site, but if i go to persona/pupils_name then everything is fine

so im not sure what is worng and i have seen searching the internet for the past 2 weeks im not a great savy for sharepoint but i do need to try and sort this

so any help i would be very greatful