If all you are trying to do is send notifiers to each of these 64 subVIs, I would suggest not doing it in a loop, but rather just placing the 64 subVIs in your diagram.
The alternative is of course to use the call by reference node and have an array of VI names. This is a little cleaner on the diagram, but 1) doesn't occur in parallel and 2) is a bit tricky. Additionally, you have to be sure that your array of filenames is correct, and that you NEVER move or rename those VIs. Of course, you could always put them in a directory and create an array by reading the directory contents.
Either way, good luck, it doesn't sound like fun.