Many issues with Dragon's Prophet can be fixed by clearing the contents of the "%userprofile%\Documents\dragoon" and "Cache" folder in the Dragon's Prophet installation directory.

Common issues with connectivity can be fixed by setting your DNS to Google DNS, or by flushing your DNS cache.

Use Google DNS (best method): Get Started | Public DNS | Google Developers
Flush your DNS Cache (may not work): How to clear the DNS Cache on a computer and web browsers?

If all else fails, restarting the computer in question can sometimes resolve issues.