Fatal error: unable to find tar archive '/var/customers/webs/ni29071_3/forum_alt/WCFSetup.tar.gz'

Information:

error message: unable to find tar archive '/var/customers/webs/ni29071_3/forum_alt/WCFSetup.tar.gz'
error code: 0
file: /var/customers/webs/ni29071_3/forum_alt/install.php (396)
php version: 5.6.29
wcf version:
date: Thu, 13 Dec 2018 02:37:12 +0000
request: /forum_alt/install.php
referer:

Stacktrace:

#0 /var/customers/webs/ni29071_3/forum_alt/install.php(913): Tar->__construct('/var/customers/...')
#1 {main}