、。
Something unexpected has come up, and I'm sorry to say I can't meet you on February 27 after all.
Literal
Anticipate-[negative-ていなかった] thing [subject-が] happen-[then-り], regrettably February 27 [on-に] [humble-お]-meet-potential-not-[change-なくなりました].
A characteristic polite apology/cancellation. 予期していなかったこと uses the past negative of ~ている — 'something [I] was not in the state of expecting.' 残念ながら ('regrettably, unfortunately') is the standard regret-opener in formal communication. お会いできなくなりました is packed: お~できる is the humble potential ('can humbly do'), plus なくなる ('to come not to be') plus polite past ました — 'has come to be that I cannot meet.' The whole arc conveys a status change from 'could meet' to 'cannot meet' politely.