I think this is a symbol setup issue, but it's not real obvious. Since forex doesn't have a trade tick, only a bid or ask tick, you likely need to specify bid, ask or mid as the bar construction type. Also, I noticed that TWS was changing the available frequencies of historical data the further I went out. I went out a week and the finest granularity was 30 minutes.
I've attached a couple of screenshots that will hopefully help.
Furthermore, as Daniel mentioned, I could not get an appreciable amount of data with a simulated account. I had to fire up my own 'live' account to get data. I know that you're using a live account, but wanted to add this confirmation for anyone who isn't.