Cant activate CS6 after change of hard drive

After a hard drive crash, we had to install a new one and reinstall cs6. After typing in the serial number there was the message (see "screenshot_1" attached.:

"Activation failed. Creative Suite 6 Design Standard cannot be activated. Product must be activated for use.

To activate the product you need a working internet connection. Check the connection settings and select repeat."

The internet connection is working! 

- I have checked the clock settings. These are OK
- The link to the activation server also shows 2 Adobe logos.
- I reset the host file, but that did not help.
- Connection to https://www.adobe.com was no problem
- GlobalSign Root CA certificate is present and activated.

Enclosed are the data of the computer:

Version: 10.11.6 (15G31)
iMac (21.5 inch, mid 2010)
Processor: 3.06 GHz Intel Core i3
Memory 8 GB 1333 MHz DDR3
ATI Radeon HD 4670 256 MB