I'm sure It is because of the line breaks in the response text. I looked into the API documentation here - http://www.barchartondemand.com/api/getHistory/queries
I tried copying the sample response from the web page to see if it can be printed to cell or not and it was working fine. So I can't debug without getting the actual response from API using the API key. If you can share API key in private then I can try debugging it.
If you look at the documentation link - They also support XML and JSON. You just have to change getHistory.csv in your URL to getHistory.xml or getHistory.json
Let me know if that helps.