I've found another problem with 5.1 UM.
If you setup a new user, and get them to 'buy access' using paypal; the transaction will go through and be accepted by UM, but when that user tries to login, they will get the error: "no valid profile found for user XXXX"
But if you get them to use a profile which is Free (£0), it works without issue.
If the user buys more time (for say £1) from the user account management page, UM will accept the payment and give them access to the internet.
So in summary what is happening when users pay (at signup) for access, they cannot log in due to the no valid profile found for.....
Can anyone else test this please?