This error most commonly comes up when one of two things happens….
The torrent exceeds 50 GB in size
One or more of the file or folder names contains an invalid character that QTM doesn't support. Check the file names and ensure that there are no strange characters. It should only have numbers, letters, spaces, dots, dashes, or square brackets. I'm not 100% sure if it supports round brackets. I believe it does, but I'm not positive on that. Apostrophes and characters with diacritical markings such as accents are the most common things to trip up QTM.