For whatever reason, Guam is not a safe place for B-2 bombers. Ten percent of all B-2s have been put out of action after serving on the Pacific island of Guam. One B-2 crashed and burned there in 2008, and another required over three years of repairs after an onboard fire while on Guam last year.
The fire did a lot more damage than the air force admitted at the time. Repair technicians were brought in, and it took 18 months to make the B-2 barely flyable. This enabled it to limp back to a California repair facility, where another two years of work will be required. The flight home was carefully monitored to avoid stress on the still damaged airframe. Many aerial refuelings were performed to keep the weight of the aircraft at a minimum. Special care was taken to avoid any turbulent weather.
The Guam Curse began in February, 2008, when a B-2 crashed on takeoff. The entire fleet was grounded for 53 days, which was how long it took to discover the cause of the first, and so far only, crash of a B-2. The remaining 20 bombers are being watched carefully
The most expensive aircraft ever, each of the 21 B-2s costs over $2 billion (development and construction costs combined). The 170 ton aircraft can carry 22 tons of bombs. There's not a big need for the B-2 at the moment, as the older B-1s and B-52s can deliver bombs cheaper, and just as reliably. Smart bombs have greatly reduced the need for heavy bombers, since one smart bomb can do the job of hundreds of "dumb" bombs. The greater accuracy and reliability of GPS guided JDAM smart bombs means that smaller bombs are now preferred. Thus a heavy bomber can carry over two hundred 250 pound SDB smart bombs. As a result, it's not unusual to only need one heavy bomber over Iraq, or Afghanistan, taking care of all requests from combat troops below.
The B-2 is stealthy, and this would be a major asset in a war against a nation with a decent air defense system (radars and missiles.) Thus the air force took its time discovering what went wrong with the B-2 on Guam (where four of the bombers were stationed), so that changes can be made to the other B-2s. The stealth aspects of the B-2 make for a very complex aircraft. Not just the tricky radar absorbing skin, but many mechanical and electronic systems as well. That's why the aircraft is so expensive, and you want to take your time trying to figure out what's not working.