"He attended a conference in our office."
Translation:Li ĉeestis konferencon en nia oficejo.
If you look at similar vocabulary in French and Spanish, you'll see that English is the odd man out here. What's more obnoxious is that "atendi" (and relevant true-friend cognates in other European languages) means both "to wait for" and "to expect" - so speaking Esperanto means learning to keep that context clear. Another pernicious problem for English speakers is that "Mi ne povas atendi" does not mean "I am eager" but rather "I can't stand around waiting."
Does "ĉeesti" (unlike esti) take an object, or did this sentence use "konferencon" to indicate direction / movement?
In one answer "laborejo" was translated as "office", which seemed a little odd but one accepts it. Then when you use that translation in another answer (such as here) it is marked wrong-even though, when highlighted, oficejo or laborejo are both suggested. Laborejo seems logically to be "work place", but what the learner needs is consistency.
This is the sort of thing that makes sense to report using the "report a problem" button, so it shows up in the admin reports. They've recently started tweaking how that button works, so it's hard to say whether it would be possible to include this kind of information in that report... but my understanding (that is, at the risk of speaking for them) is that the course admins are busy admining the course and have limited time to cruise the board looking for this sort of thing.