Answer maybe
I believe it has something to do with your host file in windows/ system32, driver/etc
You need to edit it and take out the cydia ip address first, then reboot and try it, google the cydia IP and youll find it to know what to delete
I had this problem before and that was my solution
BTW i belive its a read only file, so make sure you first go into right click properties and take it off read only to edit in notepad ++ which is what I use, then when you get rid of the cydia IP address save again as read only by doing the same in properties and then reboot
Good Luck!
PS
When you use tinyumbrella later it will put the cydia host back in there if you want after you JB and restore
Also make sure you do a full clean restore, I know the baseband will update but you can still JB if you are not worried about changing carriers like me who is on ATT