The most common issue for an import error is that your CSV files are not in the format that CryptoTrader.Tax requires.
Please refer to our guides for exporting your trading history from each exchange and follow them EXACTLY as seen. Many times, users skim them and miss very important steps. This often leads to errors.
There is also currently a known issue in Safari where file uploads aren't handled properly. Please try using Chrome/Firefox to upload your trading history file on this step.