I have been trying to subscribe my system, but "System is not properly subscribed" contiuously appears.
I've done this several times, and below is an extract from my commandline right after removing the subscription in the customer portal.
(I used "X"s for Username, id, and Pool Id for privacy reasons).
This is RHEL7 system, and I'm using Dell precision t7910.

[root@localhost aaa]#  subscription-manager register --force
Username: XXXX
Password: 
The system has been registered with id: XXXXXX

[root@localhost aaa]# subscription-manager list --available
+-------------------------------------------+
Available Subscriptions
+-------------------------------------------+
Subscription Name: Red Hat Enterprise Linux Workstation, Standard (L3-only)
SKU: RH0989838F3
Pool Id: XXXXXXXX
Quantity: 1
Service Level: Standard
Service Type: L3
System Type: Physical

[root@localhost aaa]# subscription-manager subscribe --pool=XXXXXXXX
Successfully attached a subscription for: Red Hat Enterprise Linux Workstation, Standard (L3-only)

[root@localhost aaa]# subscription-manager list
+-------------------------------------------+
Installed Product Status
+-------------------------------------------+
Product Name: Red Hat Enterprise Linux Server
Product ID: 69
Version: 7.0
Arch: x86_64
Status: System is not properly subscribed
Starts:

As troubleshooting guides note, I checked rhsmcertd state, socket numbers, and time in the system as follows.
I extracted lines from "chkconfig" and "lscpu" that seem relative to this problem.
Time display noted in "Local time" matches the actual time in Tokyo.

[aaa@localhost ~]$ chkconfig rhsmcertd
enabled

[aaa@localhost ~]$ lscpu
    Socket(s):              2

[aaa@localhost ~]$ timedatectl
          Local time: Mon 2016-04-11 19:51:58 JST
      Universal time: Mon 2016-04-11 10:51:58 UTC
            Timezone: Asia/Tokyo (JST, +0900)
         NTP enabled: yes
    NTP synchronized: yes
     RTC in local TZ: no
          DST active: n/a

Any help would be greatly appreciated.
Best regards.