I've been getting emails from cron about this error too. Last one was a few minutes ago.
CRON-APT RUN [/etc/cron-apt/config]: Thu Jul 30 07:35:24 CEST 2015
CRON-APT SLEEP: 696, Thu Jul 30 07:47:01 CEST 2015
CRON-APT ACTION: 0-update
CRON-APT LINE: /usr/bin/apt-get -o Acquire::http::Dl-Limit=25 update -o quiet=2
W: Failed to fetch http://dh2k.omv-extras.org/deb…wheezy-mirror/Release.gpg Could not connect to dh2k.omv-extras.org:80 (5.9.105.9). - connect (110: Connection timed out) [IP: 212.211.132.32 80]
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After checking, it seems like the repo is currently down.