i am using a similar filename/table load combination as you do with a knob selecting and triggering the new sample load.
looking at your screenshot, there's a big chance that your dial/controller values simply go way beyond your amount of files, so i am not sure what the muxer will do when you go past 8? if you didn't alter the code it SHOULD default to i7 for any input value beyond that but maybe double check. you have that div8 in there but that would still result in values bigger than 8.
cause i get the same error messages once i move my knob beyond the number of actually present samples. i use more of a string concat function instead of your mux approach though. maybe you wanna look into that too, more convenient than typing out every string in its own object.
whart added to this is that using a tiny midi cc pot with 128 or even more values to select
use the string/indexed object with a "0:/_biosynth/pad" prefix and a ".wav" suffix.
keep in mind here that by default this converts the number input to a three digit number with leading zeros, so you'd have to rename your files to PAD001.WAV or adapt the code of string/indexed.