The ice had gotten soft, so we had no choice but to cancel the ice skating event.

Literal

Ice [subject-が] soft becoming [because-ので] ice-skating [possessive-の] event [object-を] canceling [had-no-choice-せざるをえなかった].

軟らかくなってきた uses てくる for a gradual change. せざるをえなかった is the formal 'had no choice but to.' アイススケートの会 means 'ice skating event/gathering.'