I am not much for analyzing packet captures, but can you tell us:
1. At what point do you get the message "Socker Error: Unknown error"?
2. Is the message a pop-up or something?
3. Assuming it happens as you are attempting to start a session, run "x2golistsessions" on the server both before and after attempting to start one.
4. Install and run the "debug" build with the x2goclient installer. Run the debug build from the start menu. Expand the terminal window that is opened (so that there are as few line wraps as possible.) Reproduce the bug. Before quitting, copy and paste the output of the terminal window into a .txt attachment.
-Mike