I bet DiRT uses gzip compression of the output files. Somehow, they broke that in 7.x.x while adding compression support for something else. Yoiu know how it goes.... for every one needless enhancement, there have to be two bugs added to BOINC. I think they must be using "SCRUM" which, according to Wikipedia, "is a form of agile project management... does not require any creativity or intelligence"

Technically though, 7.0.x is still being tested. It took 34 versions before they got 6.10.x to work well, so my guess is that 7.0.x probably has a ways to go.

Important: I'm pretty sure that to downgrade to 6.x.x, you will need to abort all work, detach from all projects, and then do a complete uninstall, potentially deleting the data directory manually before attempting to reinstall 6.x.x because 7.x.x changes so much stuff that you cannot roll back to a previous version. They strongly suggested making a complete backup of the 6.10.x data directory prior to installing 7.0.x for a reason. Yep. I'm sure everyone did that, right? If you want to use bleeding edge software, prepare to bleed.