I had the same problem but i solved it . I just need to know to know your wifi security encryption . IF it is WPA-AES Xperia x8 will never get connected but if you have a WPA-TKIP , it gets connected . TRY it yourself . it worked for me . Just change the wifi settings to WPA -TKIP with the same password
P.S Change the channel to something lower than 8 or 9 because xperia hardware does not support higher channels.