From Nick at Malariacontrol.net:
It seems that the web-server was very unreliable over the last few days. As a consequence, the website and also the job scheduler here on the server could be reached only intermittently.

We have restarted the server and currently it seems to work fine. We have increased the grace period for overdue results to 3 three days to minimize the impact of this problem on your credit accounts. In addition, we have set up an additional monitoring service that will help us respond faster in case this should happen again.

We apologize for the inconvenience!
Nick

It is possible, but it means you have to constantly copy the whole BOINC (Data) directory to a computer that has an internet connection, upload & report the work done, download new work and copy that whole directory back to the machine without the internet connection.

You must make sure that the machine that has an internet connection doesn't run BOINC on its own (as copying the work from the other one to and fro will mean you have to stop and possibly remove the machine's BOINC installation) or that you run the BOINC on the connectionless machine on something like a USB stick or other removable drive.