CiviCRM Community Forums (archive)

Two things that may be going wrong. My apologies if you have already checked these. Either the extensions directory location is not writable (quite likely) or your server does not have the required zip libraries to unzip the extension (not as likely).

a) Take note of the  location of your extensions folder: http://www.yoursite.org/civicrm/admin/setting/path?reset=1

1) Check that the extensions folder is writable using your web server's control panel or your FTP program then try again.
  Assuming a UNIX server: To make it writable you will often have to give write permissions to the group.
2) Do not bother trying to to deal with the server zip setup if you are in a hurry.
  Instead find the discount module on the extensions directory, download it and unzip it locally, then upload the extension folder to your extensions folder using your FTP program.
  (See https://civicrm.org/extensions/cividiscount-extension/cividiscount-extension-3 for https://github.com/dlobo/org.civicrm.module.cividiscount/archive/v2.5.zip)
3) Remove write permissions from the extension folder again if that is the security policy that you prefer to follow.