on the website they say:

The Collatz server is currently down due to a hard drive controller failure. New hardware should arrive in the next day or two. A complete rebuild of the operating system, BOINC, and the Collatz software and project setup will then need to be done prior to the project coming back online. As this will be a complete rebuild, there is no sense hanging on to any completed workunits at this time. So, go ahead and abort any workunits you have whether they are complete or not. I expect the project will remain down for the next 10-15 days while I set it all back up and test it. Sorry for any inconvenience. And yes, I will make up for the lost credits once everything is back up and running.