New error on checkout: "known weak key for 'TripleDES' and cannot be used"

Hi,

One of our nopCommerce 1.90 sites that's been running for a while, started throwing this error.

Upon checkout, when you choose credit card, enter the card info and click "next":

Specified key is a known weak key for 'TripleDES' and cannot be used.

- Does anyone know what's happening? (other than no credit card transactions!)

(interestingly, it's the only one of our stores where we chose a different "encryption private key" than the others.  Same length, just different numbers.

thanks

David

Update:

I changed the encryption key and it now works.

It had been made 3216549832165498, so THAT is a "known weak key"?