Wyse S30 Citrix XenApp 6.5 (SSL Error 61)

Wyse S30 Citrix XenApp 6.5 (SSL Error 61)

I'm trying to connect a Wyse S30 thin client (Firmware version: 5.0 Wyse FR4 Hot Fix 3 (Build 596)) to a Published desktop in a Citrix XenApp 6.5 farm and I create a new ICA connection in Connection manager of the thin client.
In "Edit Connection Details" dialog, "server" tab I select "Published application";
The "Server location" configuration is:
Server Group: Primary
Address list:
srvw8kxweb01.mydomain (where srvw8kxweb01 is the the domain name of the citrix web interface)
SSL/TLS + HTTPS Browser

when I click Refresh I get the following error:

The server certificate received is not trusted (SSL Error 61)

I've tried also to import (via ftp) the server certificate (.cer), via the icon "Certificates" in control panel, but the error persists.

Can anyone helps me to solve this problem?

Thanks.

PS
If I point the client directly to a citrix xenapp server in TCP + HTTP Browser when I click Refresh it works and I can connect to a published desktop, but I loose the load balance capability.