Usually when I run into issues like that it is due to a char at the end of the line in the csv file. you may want to look at the .trim() function to help with the problems. to diagnose if this is your issue you can use the .length() function to see how many chars are in your variables.
One thing you might try is to just look at your variable after the failure. I.e., enter $line.source and that'll show you the value of that variable the last time it was changed. You might find that there's an illegal character in your vol name, which could happen depending on how you generated the .csv to begin with.