tradehill.com alternative?
If you have technical problems with Tradehill, your first step should be to contact them about it.

It's not clear to me in what capacity you want to replace Tradehill. If you want an exchange then Mt. Gox is an obvious possibility, or any one of the exchanges listed here. If you want an eWallet, most exchanges are good for this too, and flexcoin is another possibility. If you want merchant solutions, check out bitpay.