are you able to capture a wireshark trace of this issue? If there is any further information you are able to provide we may be able to offer more insight into why these issues are occuring.
The 408 error you are getting is usually a timeout error which means that you are not receiving any response from the server that you are trying to connect to.
This is usually caused by a router, firewall or anti-spyware software that is blocking the SIP signaling.
Normally we suggest to connect directly to modem or bypassing the firewall.
You may also need to check with your provider if you need to indicate a proxy in X-Lite Sip settings.
A 401 Unauthorized error is usually a problem with your username or password of your SIP account. I suggest you contact your SIP service provider to verify your SIP credentials. Thanks.