Are both of your tamagotchis using the connect symbol on the tamagotchi? Sometimes that won't work because that happened to me one time. Also I didn't word this right so if you don't understand this post PM me and I will help.
Are you pressing the "B" button twice when connecting? Once you see the 'Stand By' screen, you need to press the "B" button once more in order for you to connect successfully. ^_^
one of your tamas could be fake ((not to be mean)) but this has happend to me before they wont connect and both of mine are real tamas so just keep trying
also is one a v2v and another v3? if so foe the v2 you hit v1 and v3 hit others