I have just upgraded a site via the dashboard to 5.6.1.2. The updater reports that everything has gone fine, however when I try to go to the home page (index.php) I get the following errors:

Warning: require_once(/var/www/vhosts/hedonism.org.uk/httpdocs/updates/concrete5.6.1.2_updater/concrete/models/json.php) [function.require-once]: failed to open stream: No such file or directory in /var/www/vhosts/hedonism.org.uk/httpdocs/updates/concrete5.6.1.2_updater/concrete/core/libraries/loader.php on line 48

Fatal error: require_once() [function.require]: Failed opening required '/var/www/vhosts/hedonism.org.uk/httpdocs/updates/concrete5.6.1.2_updater/concrete/models/json.php' (include_path='/var/www/vhosts/hedonism.org.uk/httpdocs/libraries/3rdparty:/var/www/vhosts/hedonism.org.uk/httpdocs/updates/concrete5.6.1.2_updater/concrete/libraries/3rdparty:.:/usr/share/pear:/usr/share/php') in /var/www/vhosts/hedonism.org.uk/httpdocs/updates/concrete5.6.1.2_updater/concrete/core/libraries/loader.php on line 48

I can access any other page through the dashboard.

For information the environment information is:

# concrete5 Version
5.6.1.2

# concrete5 Packages
AddThis (1.0), Facebook Like Button (1.1), ProEvents (6.2.2), Superfish (1.1.5), Tweetcrete (1.6.5).

# concrete5 Overrides
css/style.css, css/winxp.blue.css, css/tabs.css

# Server Software
Apache/2.2.3 (CentOS)

# Server API
apache2handler

# PHP Version
5.3.18

# PHP Extensions
apache2handler, bz2, calendar, Core, ctype, curl, date, dom, ereg, exif, fileinfo, filter, ftp, gd, gettext, gmp, hash, iconv, imap, json, libxml, mbstring, mcrypt, mhash, mysql, mysqli, odbc, openssl, pcre, PDO, pdo_mysql, PDO_ODBC, pdo_pgsql, pdo_sqlite, pgsql, Phar, Reflection, session, shmop, SimpleXML, snmp, soap, sockets, SPL, standard, tokenizer, wddx, xml, xmlreader, xmlrpc, xmlwriter, xsl, zip, zlib.

# PHP Settings
max_execution_time - 30
log_errors_max_len - 1024
max_file_uploads - 20
max_input_nesting_level - 64
max_input_time - 60
max_input_vars - 1000
memory_limit - 128M
post_max_size - 10M
safe_mode - Off
safe_mode_exec_dir - <i>no value</i>
safe_mode_gid - Off
safe_mode_include_dir - <i>no value</i>
sql.safe_mode - Off
upload_max_filesize - 10M
mysql.max_links - Unlimited
mysql.max_persistent - Unlimited
mysqli.max_links - Unlimited
mysqli.max_persistent - Unlimited
odbc.max_links - Unlimited
odbc.max_persistent - Unlimited
pcre.backtrack_limit - 1000000
pcre.recursion_limit - 100000
pgsql.max_links - Unlimited
pgsql.max_persistent - Unlimited
session.cache_limiter - nocache
session.gc_maxlifetime - 7200
soap.wsdl_cache_limit - 5
safe_mode_allowed_env_vars - PHP_
safe_mode_protected_env_vars - LD_LIBRARY_PATH

Aarrgghh! Help!