When you say it won't accept characters, do you mean it gives an error message or that it only has room for 13? I'm assuming your device is like my Axim and just shows asterisks in the key field and if it seems to only have room for 13, you can probably input more - the entries scroll as you type.

If you cannot get it to work, you might consider switching to 64-bit. In practical terms it is just as secure as 128 and it's much easier to get 10 characters right.