2 Asterisk boxes : 1 can see the other, not vica versa

Asterisk-server 1 :

register => hostedasterisk:pass1@domain2.biz

[BOX-YOCAN]
type=user ; incoming from YOCAN…
auth=rsa
inkeys=Key ; pub key of user
secret=XXX ; pass2 of YOCAN
context=from-BOX-YOCAN ; incoming from YOCAN
trunk=yes
transfer=no
qualify=yes

[BOX-YOCAN]
type=peer ; outgoing to YOCAN…
host=dynamic ; registers
auth=rsa
outkey=kEy ; private secret key
username=hostedasterisk ; username @ YOCAN
trunk=yes
transfer=no
qualify=yes

Asterisk-server 2 :

register => BOX-YOCAN:pass2@ip_hostedasterisk

[hostedasterisk]
type=user ; incoming from Hosted Asterisk
auth=rsa
inkeys=HoStAsTkEy ; pub key of AsteriskHosted
secret=XXX ; pass1 of HostedAsterisk
context=from-HostAst ; incoming from HostedAsterisk
trunk=yes
qualify=yes

[voipcenter]
type=peer
host=IP of HostedAsterisk
auth=rsa
outkey=Key ; private secret key
username=BOX-YOCAN ; username @ HostedAsterisk
trunk=yes
qualify=yes

Asterisk-server 2 (YOCAN) registers well to Asterisk-server 1 (AsteriskHosted) but registration of Asterisk-server 1 (AsteriskHosted) is rejected by Asterisk-server 2 (YOCAN). Why is that ??

Jonas.