How can I sell BTC on Ripple com? I have just been helped by a friend and got 300 XRPs (which quickly became 299, thank you) and then I transferred 1 BTC from another address to my Ripple.com wallet.

First Ripple.com shows 299 XRP and has an exclamation sign next to it, which clicked says "Your current account is low. You must keep a minimum of 250 XRP to use all the features of a ripple." 

Great! I am about to trust somebody for whom 299 &lt; 250 ? Or is it advance warning?

But I digress, that is the new world of cryptocurrencies, some of the worst Web and UI and database programming seen in the recent history, so a site that clearly says it is beta must be excused.

Okay, so now I am trying to sell my 0.5 BTCs for some XRPs. Whether I place BTC sell order at the current bid, or in the middle between current bid and ask I always receive;

Error: Transaction failed
You don't have sufficient funds
Your current account is low. You must keep a minimum of 250 XRP to use all the features of Ripple.


That is a warning shown whenever your XRP balance is less than twice the current reserve requirements. The number in the warning will also change as you add/remove trust/credit lines or add/fill/cancel trade offers.

The amount of XRP required to in reserves are listed on the Ripple wiki. Basically, the 250 you see is 200 for your account plus 50 for your trust/credit line to Bitstamp (that you added to get Bitstamp-BTC into your Ripple account).

To make a trade offer requires an additional 50 XRP (which is just a reserve, it becomes un-reserved when the offer is filled or cancelled). Since you had only 299.9999 XRP (not 299 as you said) Ripple was unable to create a new trade offer as the new reserve limit would have been 300. Yes, the error message is not as clear as it should be.

Whoever sent you your initial 300 XRP really should have sent 300.1 or 350.1 (or more). Although it is possible to get more XRP from BTC on a new Ripple account with only 250.0001 XRP, it's requires careful management of the limited XRP that shouldn't be expected of a new user. It's really best to start a new account with at least 350.1 or more XRP.