License issue

Dear Sir/Madam

I purchased Red Hat Enterprise Linux 1-year Subscription from your website on septembre 5th, 2015
I could download version 7 and 6 and I installed version6.
Today I encounter system issues and I installed again version 6.7 on the same server.
When I issue the command yum and I got the following error,message

This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.

Could you help to resolve this issue ?

thank you in advance .