The pre-launch combustion test won’t be carried out until after July 27, according to the Khrunichev State Research and Production Space Center in Russia, which is responsible for the first stage of the rocket.
“The center was scheduled to perform a combustion test on July 23 but the center notified us that the test would have to be delayed until after July 27 because of technical problems,” said Lee Sang-mok, an official of the ministry on Thursday. “This means we will have to put off the launch for four days or more.”
Lee added that the center called for renegotiations on the launch schedule once the center had completed the combustion test.
Under the current plan, the Russians should conduct the test in order to check the performance, safety and other systems critical for a successful launch of the space rocket.
This is, as another article reminds, the third delay of the launch. It was scheduled first for December, 2008, then for March, and then for July 30th. According to that Korea Times article, the launch was originally delayed because of an earthquake in China that slowed delivery of parts, and was delayed again in March because of safety concerns. Here's an interesting paragraph from an April article:
Out of the eight countries that have launched a rocket with their own technology, only three - Israel, France and Russia (Soviet Union) - have succeeded in their first try. South Korea’s own track record in developing space technology is short. The country launched its first satellite in 1992, from French Guiana. After that, nine more satellites have been launched but all with overseas technology.