Xshell not switching GNU Screen windows [1]

Used google-fu but to no avail. When I try to switch windows in GNU screen over an SSH connection, using ctrl+a, method, it just enters the number I pressed into the terminal. Strangely I can still detach my screen session using ctrl+a,d.

Program Ver. : Xshell 4

... And here I discover that I can use the number row at the top but not the 10-key number pad that I am accustomed to... strange.