OpenVPN client error : Failed to configure TLS context

I got this errors when trying to start my openvpn client:

Tue Nov 28 15:28:03 2017 us=942328 OpenVPN 2.3.14 arm-poky-linux-gnueabi [SSL] [LZO] [EPOLL] [MH] [IPv6] built on Sep  6 2017
Tue Nov 28 15:28:03 2017 us=942837 library versions: LibreSSL 2.5.0, LZO 2.09
Tue Nov 28 15:28:03 2017 us=943095 WARNING: file '/etc/openvpn/auth.txt' is group or others accessible
Tue Nov 28 15:28:03 2017 us=951558 WARNING: No server certificate verification method has been enabled.  See http://openvpn.net/howto.html#mitm for more info.
Tue Nov 28 15:28:03 2017 us=951835 PO_INIT maxevents=4 flags=0x00000002
Tue Nov 28 15:28:04 2017 us=452047 Failed to configure TLS context
Tue Nov 28 15:28:04 2017 us=452305 Exiting due to fatal error

It is not a firewall issue since I deactivated to be sure. I used the same configuration on another ARM client and it is working.

Here is the config file:

dev tun
tls-client    
remote myRemoteIP 1194    
pull    
proto udp    
script-security 2    
ca /etc/openvpn/ca.crt    
comp-lzo    
reneg-sec 0    
cipher AES-256-CBC    
auth SHA1    
auth-user-pass  /etc/openvpn/auth.txt
log-append /var/log/openvpn.log
verb 9

any ideas what is going wrong? thanks