I'm not ruling out the possibility that someone somehow forgot to pay for the gas, but the overall context was that this was a hugely unpopular gas deal attacked in Egypt as a sweetheart arrangement selling gas cheap to Israel - the pipeline's been blown up more than a dozen times since the Egyptian uprising, the now-ruling Muslim Brotherhood was against the deal, etc.
To quote the late-April AP story,
Ibrahim Yousri, a former Egyptian diplomat who had brought the issue to court, welcomed the decision announced Sunday.
“It has become a scandal bigger than the (ruling) military council can withstand,” Yousri said. He said there are gas shortages in Egypt, and growing economic woes, further enflaming popular unrest. He called the business deal a “treason” to national interests, adding, “This is a great political step.”
And Egypt's apparently offering to sell gas, at a "new" price, I'm guessing higher than that in the 20-year contract they say Israel broke. Cui bono? Of course, if the deal was a rip-off for Egypt signed by a now-deposed dictatorship, their abrogating it isn't the most controversial thing in the history of post-revolutionary commerce.