There are a couple of things that might be going on:
2015-09-28T17:11:33+00:00 ERR (3):
exception 'Zend_Mail_Exception' with message 'Subject set twice' in /var/www/vhosts/theshowerdoctors.ie/httpdocs/lib/Zend/Mail.php:933
The last line in exception.log is this. Seeing the stack trace, I would disable the extension
Mage_Advancedsmtp. To do this, open
app/etc/modules/Mage_Advancedsmtp.xml, and change the value of the
<active> node to be
I don't think this is causing a problem, but it looks to be there is a problem with permissions for your LESS files. Your LESS compiler is triggering an exception, as it can't find the files to compile. Since there is no URLs logged with the stack trace, I can't tell whether this is also causing the problem.
Exception.log: exception 'Exception' with message 'load error: failed to find ...'
System.log:Warning: is_file(): open_basedir restriction in effect. File(.../skin/frontend/mtbelano/default/css/_config/design_default.less) is not within the allowed path(s): (/var/www/vhosts/theshowerdoctors.ie/:/tmp/) in /var/www/vhosts/theshowerdoctors.ie/httpdocs/lib/Soczed/less/lessc.inc.php on line 2378
This is a PHP
open_basedir() issue. The php script cannot access the LESS file. If this is what is causing the problem, then your web host probably changed permissions on your server, which would cause the problem.