How to stop green light flashing (& set alarm)?

I have a Veritas8 alarm panel which has been brilliant over the years. This morning I got up and the alarm had been set overnight to exclude the landing (as normal) However, when I entered my code, the green Unset light kept flashing - and will not stop. I tried a full set to see if that would help but the beeping kept going and the system did not set. Any suggestions?

Many thanks