The filename should contain a version, e.g. 14.0; 14.1; etc. Otherwise you can check with this command:

turnkey-version

Also we have had a few issues with the (yet to be officially released) v14.1 images, although I was not aware of any specific issues with ownCloud.

Also it would be worth checking the Apache logs as perhaps there is something of value/interest there. Try this:

tail /var/log/apoache2/error.log

If it doesn't make any sense to you please feel free to post it here.

Finally I has been discovered that as of v14.0/Debian Jessie PHP5 is precompiled to include a php cache tool (Zend's OPCache), but our build code install xCache (an alternate php cacher). Whilst not ideal, for most php applications it doesn't cause any issue, however we have discovered that it does cause issues with some software. No one else has reported this issue with ownCloud, but maybe something unique to your situation, or a recent update has caused it to become an issue now? To see if xcache installed do the following:

apt-cache policy php5-xcache

If it has a version number next to "installed" then you do have it installed and perhaps it's worth removing it? Removing it shouldn't do any harm - worst case it just won't fix the issue. Try this:

apt-get purge php5-xcache
service apache2 restart

While testing Owncloud (iso) I ran into the same issue after I updated things.  I'm in the midst of starting over just to eliminate some of the results of my thrashing around but am not back to where the issue occured yet.  However in my thrashing I found several posts like this.  Don't know if it applies to  your situation or not but you might want to check it out.   https://github.com/owncloud/core/issues/14023

Pat