SEATTLE — Washington’s health care exchange shut down after the first few hours of open enrollment Saturday as state officials and software engineers tried to resolve a problem with tax credit calculations.Officials at the exchange said Washington Healthplanfinder appeared to be working fine at first. When the exchange’s automatic quality control system reported the problem, they decided to shut the whole system down at about 10:30 a.m. to fix it.The tax credits were off by just a few dollars in some cases, exchange CEO Richard Onizuka said. He said the system would remain down until it can give consumers who want to buy health insurance accurate information.Spokeswoman Bethany Frey suggested consumers try again on another day.Open enrollment for health care insurance continues through Feb. 15, and officials are hoping as many as 85,000 people sign up. They also hope all of the about 145,000 people who bought insurance during the first open enrollment period, which began Oct. 1, 2013, will renew for another year.Those who run the exchange had been hoping their computer system would handle traffic better than it did last year, when it shutting down and rejected applications for reasons like a hyphen in a last name. About a thousand people who bought insurance the first time around are still having problems getting their payments credited and that money transferred to their insurance companies.