"It must not happen!"
Translation:Det må ikke ske!
Why is it ske and not skete? According to Verbix, that's not a proper conjugation of the verb. Is Verbix not to be trusted? :(
There is no verb in Danish called "at skete". "Skete" is the past tense form of the verb "at ske". Verbix usually works well for words it recognises and when it's in the infinitive form, otherwise it will guess based on standard conjugation rules, which it was trying to do with "skete".