Click on Safari and select Reset Safari...
Click on the Gear icon in the upper right of the screen and select Reset Safari...
- In the screen that appears, ensure that Clear History, Remove all webpage preview images, Empty the cache, Clear the Downloads window, Remove all cookies, Remove other AutoFill form text, Close all Safari windows, and Reset all location warnings have been checked (the options may vary depending on the operating system you are using - see the screenshot below).
3. Click on Reset.
4. Restart Safari and try the website you were having trouble with again to see if the problem is resolved.