1. Open Internet Explorer.
2. Set it as your default browser(Internet Explorer is what Combat Arms uses to get the clan information).
3. Go to tools-> Internet Options.
4. Go to delete under browsing history.
5. Delete Preserve Favorite Website Data, Temporary Internet Files, Cookies, and History.
Then open up combat arms and the clan server error should be fixed. If it isn't, there is another step.
6. Add nexon.net to your trusted sites(doesn't always work, but helps if the others didn't)
If this helped, a reminder to leave a thanks and have a good day.