If you experience issues when trying to upload the latest FreePBX Asternic CDR module into FreePBX version 13, here is a recipe to install the module via the command line that seems to work:
First log into the server via ssh, then run this commands:
#> fwconsole ma delete asternic_cdr #> fwconsole ma downloadinstall <a href="http://download.asternic.net/asternic_cdr-1.6.3.tgz">http://download.asternic.net/asternic_cdr-1.6.3.tgz</a> #> fwconsole chown
That would reinstall the latest Asternic CDR FreePBX module and make it available.
Thanks to James Cocke for the information!