OH noes! I took another trip to the bathroom and thought to myself "What could be wrong?" I checked the files over and over again and BINGO BANGO BONGO! I found the problem. The .wav file was too LONG. I realised this cuz all the extended themes did not work. It would be deleightful if you could tell me the limit, my guess is around 20 minutes but a more exact time would be helpful! Thank you for your time (even though i figured it out but ur time is still required!)
I'm glad you were at least able to figure out what was wrong. And yeah, it's not surprising there's a size limit. I can attempt to brute-force looking for the largest possible size programmatically which shouldn't be too hard. I'm guessing it's a file size limit and not a duration limit. I'll report back with my findings and add the information to the forum and GitHub page.
Edit: Here's my findings. It seems the hard limit for supported wave file sizes is just under 256MB. This size being referred to is the data size of the audio data itself and not the details about the audio. Anything at that number or higher will throw the same error you were encountering.
I'm now testing the upper limits of how many 256MB wave files can be written to a Wave Bank before it fails.
Edit 2: Final tests show that Terraria will except a Wave Bank of 41 waves of maximum size (I was pretty surprised). And these waves are completely randomized bytes so I doubt the compression was able to do much. The final wave bank size was 358MB. I ended my tests at 58, 256MB wave files but I haven't seen a limit on how many waves can be packed in using XactBld, whatever the case, it's irrelevant to test this unless used for games outside of Terraria. I have updated the main page with all of my findings.
Anyways, if anyone wants a Wave Bank made of pure static, then I'd be happy to deliver.