I tried for more than a day, but I was unlucky. Whenever I switched to pool mining for a few hours though, my miners found a few blocks...

I gave up on solo mining for now, as I get about 150,000 coins per hour pool mining and according to this difficulty it would take about 3 hours for my miners to find one block. One block can only be worth max. 500,000 coins. Pool mining for 3 hours gives me around: 3 * 150,000 = 450,000. Plus when you are solo mining you might not always get the biggest block rewards (like 25,000) , whereas when you are pool mining it is spread much more in your favor.

My 5 cents...