Cannot open attachment

Version 6.5.11

We migrated our SugarCRM app to a new server, and while everything else is running fine, we found that the attachments uploaded cannot be opened, giving error in the log:

[Mon Oct 12 03:05:18.260478 2015] [core:error] [pid 49957] (13)Permission denied: [client 219.92.23.52:55972] AH00132: file permissions deny server access: /var/www/vhosts/crm.smssb.com/cache/jsLanguage/en_us.js, referer: http://crm.smssb.com/index.php?action=ajaxui

The user can view the attachment as successfully uploaded but when trying to open the file they see the below error in the web page:
This document is missing a file, most likely due to an error during upload.

How can I solve this?