My friend just had this problem. According to him, he was advised to uninstall Akamai and then try. He is back in game.
There seems to be a lot of causes for this error including Windows UAC.
For me, when I had this error, this worked for me:
1. DO NOT uninstall DDO!!!
2. Go to
http://www.ddo.com/en/game/download and choose Play Instantly. This will start a download from Happy Cloud.
3. As soon as minimum download completed (about 485 MB) STOP download and uninstall Happy Cloud software.
4. Start DDO client and let it update.
5. Play DDO
Good luck!!!