I’ve had this specific error message, a lot of time. I also had, in the same time, a positive balance, juste like you.
If I understood correctly, that positive balance isn’t taken into consideration, as you’re in test mode.
So, as ar as I’m concerned, the solution was to use the account number I gave you in my first answer.
Unfortunatly, if this doesn’t work for you, I’m afraid not to be able to help…
Hope someone else will find this out.
Michel