Maybe, you could try to do the followings if any of these could help fixing your issue:
- Use a different browser.
- Make sure the Adobe flash player is up-to-date, and also allow it to access DDTank.
- Clear your browser cache and cookies.
Connection problem from your internet can also cause this.
Making you dc-ed/get booted from the server and then the page refreshes.
Hopefully, those can fix your issues, or maybe, someone else who knows better about browser issue can give you a better assistance ^^