There's been a problem.
'C'è stato' — cheh STA-to. The contraction 'c'è' is essential — don't say 'ci è'.
Use when something has genuinely gone wrong and you need to cancel urgently. This phrase signals seriousness without going into detail and works in any context.
'C'è stato' is the passato prossimo of 'esserci' — literally 'there has been'. 'Un problema' means 'a problem'. The vagueness is intentional and acceptable in Italian social culture.
È successo qualcosa.
Something has happened.
Even more vague — suitable when you genuinely can't explain
Ho avuto un problema con la macchina.
I've had a problem with the car.
Specific version — car trouble is a universally accepted excuse
Si è rotto qualcosa in casa.
Something broke in the house.
Suggests a domestic emergency — no one will question this
Italians are generally curious and may press for details, but saying 'ti spiego dopo' (I'll explain later) is an accepted way to defer the conversation. Following up with an explanation later is expected and shows respect.