The exhibition was canceled because one unexpected thing after another kept happening.

Literal

Unforeseen-[classical-ぬ] occurrences [subject-が] one-after-another occur-[past-so-ので], exhibition [topic-は] cancellation [become-になった].

Two common patterns. 次々と ('one after another, in rapid succession') uses the doubled adverb 次 ('next') plus the adverbial と — a productive pattern for repeated or sequential action (続々と, 段々と, 堂々と). 中止になる ('to be canceled,' literally 'to become cancellation') is the standard way to report a cancellation as a change of state, distinct from 中止する ('to cancel').