Nsupdate, getting BADKEY error

I'm trying to update a name using nsupdate executed from within the name server itself but I receive the error message
; TSIG error with server: tsig indicates error.

I created a key with dnssec-keygen -a hmac-md5 -b 512 -n HOST -r /dev/urandom dyn.mydomain.com. and copied the secret into the named.conf.

My named.conf is as follows

key "dyn.mydomain.com." {
   algorithm hmac-md5;
   secret "T2DjtGkGAzPAVrL6zar9GpxjNQ1iOjJzWKhPsF5gu0xQbaONhK7ZmC0n WKatgbGEHqla1uoxG3FdktQPolMIjQ==";
};
zone "dyn.mydomain.com." {
   type master;
   file "/var/cache/bind/dyn.mydomain.com.hosts";
   allow-update {
       key "dyn.mydomain.com.";
   };
};

The file dyn.mydomain.com.hosts looks as follows:

$ORIGIN .
$TTL 8400       ; 2 hours 20 minutes
dyn.mydomain.com  IN SOA  ns. root. (
                           2007072513 ; serial
                           7200       ; refresh (2 hours)
                           900        ; retry (15 minutes)
                           1857600    ; expire (3 weeks 12 hours)
                           8400       ; minimum (2 hours 20 minutes)
                           )
                   NS      ns.dyn.mydomain.com.
$ORIGIN dyn.mydomain.com.
ns                      A       [ip of this name server]
$TTL 60 ; 1 minute

I restadt bind9, then use

nsupdate -v -d -k /etc/bind/Kdyn.mydomain.com.+157+53489.private
> server localhost
> zone dyn.mydomain.com
> update add test.dyn.mydomain.com IN A 80.80.80.80
> send

Sending update to 127.0.0.1#53
Outgoing update query:
;; ->>HEADER<<- opcode: UPDATE, status: NOERROR, id:  50553
;; flags: ; ZONE: 1, PREREQ: 0, UPDATE: 1, ADDITIONAL: 1
;; ZONE SECTION:
;dyn.mydomain.com.                   IN      SOA

;; UPDATE SECTION:
test.dyn.mydomain.com.       60      IN      A       80.80.80.80

;; TSIG PSEUDOSECTION:
dyn.mydomain.com.            0       ANY     TSIG    hmac-md5.sig-alg.reg.int. 1325777156 300 16 5k3AkgLuCziNKtaeb39MRE== 50553 NOERROR 0

; TSIG error with server: tsig indicates error

Reply from update query:
;; ->>HEADER<<- opcode: UPDATE, status: NOTAUTH, id:  50553
;; flags: qr ra ; ZONE: 0, PREREQ: 0, UPDATE: 0, ADDITIONAL: 1
;; TSIG PSEUDOSECTION:
dyn.mydomain.com.            0       ANY     TSIG    hmac-md5.sig-alg.reg.int. 1325777156 300 0  50553 BADKEY 0

What can be the reason?