Have been playing around with Membrr (subscription ecomm) and ran into a problem where a new subscription could be purchased but the user is denied when they return to login, error being that their account is not activated yet.
This would persist even though new accounts were set to No Activation. Letting EE send activation emails would be troublesome with Membrr because it inserts a new member upon every attempt at purchase, then deletes if validation fails. So you would have lots of bogus activation emails. It is certainly a plus though that users have their account generated on purchase (vs EE.com style, create account first).
The real problem turned out to be: trying to repurpose the default member groups. I had set the “Grant Access” group as #4. Group #4 is set up to return the activation error (I think it is Pending group?). Just make more member groups.
So if anyone else gets this problem, hopefully the above will help you!