There can be many causes to this. Try a few of these fixes to see if they help.
1. Scan for viruses/malware (Just in case)
2. Do clear cookies/history/temp files/etc on the browser your using. (If this don't work; try a differentt browser.
3. Try shutting down your security on your computer just to see if it fixes it. If the problem still occurs after that, make sure to turn security back on.
4. Contact support. Sorry
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