Your audio duration should be fine!
After experimenting with a deck where I have a similar audio looping setup I think my best guess is that the script is expecting to find a Field that has the name "loopcounter" on the same card you're on and it's not finding it so it can't correctly loop through your clips.
(Because nothing is loopcount-ing, y'know?)
It could be that it doesn't exist, or it has a typo in the name or it does exist by that name but it's on another card... something like that.