TOPIC: No iDeal payment possible

iDeal payments all end halfway with following error:

Foutmeldingenlijst:
* Klantmelding: Betalen met iDEAL is nu niet mogelijk. Probeer het later nogmaals of
betaal op een andere manier.
* Foutmelding: Received XML not valid
* Foutdetails: Field generating error: The reference to entity "O1503387"
must end with the ';' delimiter.

Anyone have a clue?

Found it:
I use a registration number prefix: J&O
Apparantly iDeal doesn't like the use of a & here