I have two almost identical Haswell machines, both running Ubuntu 16.04. One one, I am running QC with no problems:
http://www.gpugrid.net/results.php?hostid=357332

On the other, I am now getting Python errors:
http://www.gpugrid.net/results.php?hostid=334241&offset=0&show_names=0&state=0&appid=30

The errors started a couple of days ago, when I started to run Folding on the GPU, which also uses python. That seems to have triggered it, though it may have been something else. Also, I have just performed an update of everything on Ubuntu on this machine, which included a python update of some sort. It didn't fix it, but may have sealed the nail in the coffin. (I have stopped running Folding on this machine, but the damage may have already been done, whatever it is.)

Important questions (for me to understand):

1. Has the "working" machine also been updated?
2. Did you follow those "advanced" FAH install instructions?

In the meantime, try resetting the project: this deletes all traces of "our" python environment and downloads it again.

I get python 2.7.13 on both Linux boxes, where on the laptop with no GPU board the
QC 3.21 tasks execute and validate, while they fail on the SUN WS which executes GPUGRID GPU tasks.
Tullio

BOINC on boinc.berkeley.edu site for Linux is still 7.2.42. I am using BOINC 7.8.3 dpwnloaded from a SETI user, this is why of its strange location. But it works on GPUGRID GPU tasks and on LHC@home Atlas tasks, which need VirtualBox, installed.Next week I shall have new version of SixTrack CPU tasks from CERN.
Tullio
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BOINC on boinc.berkeley.edu site for Linux is still 7.2.42. I am using BOINC 7.8.3 dpwnloaded from a SETI user, this is why of its strange location. But it works on GPUGRID GPU tasks and on LHC@home Atlas tasks, which need VirtualBox, installed.Next week I shall have new version of SixTrack CPU tasks from CERN.
Tullio

SuSE is not following much BOINC, so I have to find newer versions where I can. But 7.8.3 is working well on my two Linux boxes, all with SuSE Leap 42.3 64 bit.
Tullio

The repository versions should all be updated to the recommended new release v7.10.2 by now.

These versions all run in a secure sandbox and support all BOINC features.

Berkeley provided a stand-alone, less secure, version for use on Linux distributions with no repository support for BOINC: this is the version which is stuck at v7.2.42, and is unlikely to be further developed. This version runs in user space.

Some users are prepared to trade off the added security of the repository versions for the extra flexibility of running in user space, and users are welcome to download to download the source code and compile user-mode binaries for their own use. But these private builds are not supported by the BOINC writing community, and you'll need to make your own support arrangements if you need them. There are communities of interest all over the internet - not always conducted in English - where this sort of mutual support is available.

The repository versions should all be updated to the recommended new release v7.10.2 by now.