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Ah, your configuration might have blocked fragmentation. If so, that would have broken your CCTV.
Unless your MTU really supports 1500, setting it such might allow fragmentation "transparent" to the sender.
Although your CCTV is now working, also if supported MTU isn't 1500, data traffic might be needlessly fragmented too.
If you've not already seen it, you might find this Cisco paper helpful: http://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html
