I found a way around this problem. I think the issue is with the encryption. In sites/all/modules/ubercart/payment/uc_credit you need to modify the encryption functions. At around line 534 you will find a line of code that reads:
$_SESSION['sescrd'] = $crypt->encrypt($key, serialize($order->payment_details));
Change this to:
$_SESSION['sescrd'] = base64_encode(serialize($order->payment_details));
(I know, its less secure, but it WORKS)
Then around line 1284 look for:
$cc_cache = unserialize($crypt->decrypt($key, $data));
Change this to:
$cc_cache = unserialize(base64_decode($data));
and it should work for you.
NOTE: These are not exact line numbers. I have debugging code commented out in my code, so you will have to look for the specific code that I indicated above.
Message me if you need any more help.