Invitation no longer valid

Dear community,

ever since the disaster at NetGear that screwed up the ReadyCloud access I have been trying to reinstate the user who has share access to my volume. I have tried disabling and then re-inviting the user, but every time they click on the link in the e-mail, they just get the message "Confirm Invitation (X) The invitiation is no longer valid". This is literally 2 minutes after receiving the e-mail.

I have seen other posts but no actual solutions, apologies if the solution appears somewhere else on the community - just point me to it :-)

Thanks,

Graeme