Unable to log back in after creating a user, null as part of the Claims Process

[paulinventome]

Not sure if it's just me doing something wrong but i can create a user no problem (and then use that straight away). But if i log in again with that user i get:

ArgumentNullException: Value cannot be null.
Parameter name: value
System.Security.Claims.Claim..ctor(string type, string value, string valueType, string issuer, string originalIssuer, ClaimsIdentity subject, string propertyKey, string propertyValue)

As far as i can tell the actual document stored seems okay. So i'm a bit confused where this is coming from.

Any pointers?

thanks
Paul