Missing .sof

We have several projects all using Quartus II V7.1Build 178 (SP1).

For some reason this week, a full compilation is not generating a sof output file.

The compiler goes through all the normal stages and shows no errors, but there is no output file.

This is now being seen on 2 separate machines.

Has anyone else seen this? Is there something we can do about it?

Upgrading to a newer version of Quartus is not an option.