Come the end of the year, the office is busy nonstop.
Tips
grammar
Verb + 不了 says the action cannot happen at all; with 个 in between it says it goes on and on. Several have become words of their own: 受不了 'can't stand it', 免不了 'unavoidable', 少不了 'indispensable', 大不了 'at worst'.
mistakes
Here 了 is 'to finish, to manage'. A polite 'no thanks' is 不 + the particle 了: 不了,谢谢 'no, thanks'.