@morrow without logs this will be hard to track down. can you ask your administrator to open up a support case for this?
You can get an Archiver license for as many users as you want, but minimum 20. The amount of Archiver users does not have to be equal to the amount of Zarafa users, but it must be less. So if you have a Zarafa license for 100 users, you can get an Archiver license for anywhere between 20 and 100 users (in multiples of 5).