The reason is most likely that you have not been added to the committee in Prepare. Contact the person responsible for the meeting agendas or the administrator of Prepare in your company to gain access.
It could also be that you have access to multiple organisations in Prepare and that you are under the 'wrong' organisation. Click the 'back' button in the top left corner until you come to the list of organisations and choose the 'correct' one.
Note, all closed committees can only be seen by their members. The closed committees will never appear in the "other committees" list.