I have certainly loaded numerous different wav files into the MODX without involving any additional software. I guess something in the file does not go well with the MODX. Maybe the sample rate? Did you check if 48 kHz is supported? I suggest you try other files to see if they work.

24-bits? 16-bits? 8-bits? Stereo? Mono? There's more to wav files than one parameter.

Never had this problem on the motif, or motif es regardless of where the wav. came from, or what the bit resolution was.

What exactly are the wav. file specs required to load into the modx?

Might I have a defective modx7?

WAV (44.1 kHz/24 bit/Stereo or 44.1 kHz/16 bit/Stereo) - this is the same as with its predecessor, Motif XF.
.wav and .aif files can be loaded. They are converted to MODX Waveforms upon Loading; they are converted to 44.1kHz. The MODX gives it an original Key, a Key Range, and Velocity Range.

Sorry, you are having difficulty. Did they list MODX/MONTAGE as compatible synths for these .wav Files?
Do you have any other attributes other than the original Sample Rate..?

All Yamaha Synthesizers capable of loading .wav Files, including the Motif classic and Motif ES, had specs for compatible wav Files - back then you didn’t have 24-bit compatibility but maximum Sampling Frequency was always 44.1kHz. The Motif and Motif ES both featured a Sampler... and while you may have been able to input a 48kHz signal they had a SRC (Sample Rate Converter) which converted it immediately to 44.1KHz. The MONTAGE/MODX do the same thing... a 48kHz .wav can be loaded ... it will be converted and played back at 44.1kHz (it will sound about 8% lower in pitch)

The MOXF, MODX, MONTAGE do not have built-in samplers. They are playback only.
It’s been asked but not answered... what are the attributes of what you’re trying to load.
Sample Rate
Bit Resolution
Size

An illegal file error message would be shown when the data does not meet the criteria.
And let me fully understand, these wav Files - are you saying you can load them into a Motif and Motif ES, and they load there fine but not to your MODX? That’s happening now, or are you remembering that you used to Load 48kHz data into those keyboards back-in-the-day?

Either way, you should be able to load 48kHz data, if it meets the other criteria. Let us know.

These are the same wav. files that load on my korg Kronos, most are created with a korg Kronos, onto my kurzweil pc3k6 and motif and motif es.

Also I want to mention that the modx loads mid. files Without any problems

So you don’t know the specifications of the .wav?

@Ernest

I can't tell if you have a Mac or a PC. I have a PC - and that's what I'm familiar with. If you have one too, download something which will inspect your WAV file and tell you its properties. One of my favorites is wavosaur. It's free and doesn't nag you. There's nothing to install - it's an EXE file that runs without need to install. I use the 64-bit version downloaded from the main website: https://www.wavosaur.com/

When you load a file, you can click on the "File" menu then "Properties". It will output something like this (the window allows for you to copy the contents or lets you export a TXT file):

	General information:

		Sample name:		C:UsersJasonDocumentsSKYLIFESampleRobot6DataStartupProjectsVP_AiryDrone - Velocity 127 - 028 - e0.wav

		Channel number:		2

		Sample number:		463050

		Total duration:		00:00:10:500

		Frequency:		44100Hz

		Bits per sample:		24

		Format:			PCM

	Selection:

		Selection start:		0

		Selection end:		0

		Delta:			1

	No loop points

	No marker points

	No automation points

	

This file comes with Samplerobot. It would be nice to have the filesize - but I can roughly calculate it. 24 bits per sample - that's 3 bytes per sample (24/8=3). Two channels (stereo). And 463050 samples. I calculate: 2 channels * 463050 samples * 3 bytes/sample = 2,778,300 bytes

When I look at the file size on my hard disk, I see:

08/12/2018  03:02 AM         2,778,360 VP_AiryDrone - Velocity 127 - 028 - e0.wav

Matches almost completely. The extra 60 bytes are for the WAV's header - which includes the magic bytes, loop points, framing, etc. Close enough.

Therefore - from this "properties" copy, I can derive everything necessary to answer the questions we've been asking about your sample. I am modeling the level of detail of an answer that would be helpful for you to provide. And, if you have a PC, giving specific instructions where you can download such a tool to provide this information.

Telling us other platforms where these wav files work does not help you. I can empathize that it would be nice if the instrument would, at least, give you a better error message. Something telling you what's wrong with the WAV - which parameter(s) do not match what MODX needs. Even better would be to convert the sample into something that is usable - likely what the other keyboards do. MODX has no sample memory -- which could hinder the ability for MODX to do this conversion vs. the other keyboards you have used. Mostly which have sample memory on-board to handle manipulating a sample. So there may be technical limitations to what MODX can do. That aside, I do think the error message is frustratingly terse where it could tell you something immediately actionable - like your bits per sample are not within range. Or your file size is too big. Or your encoding scheme is not supported. Or there's something wrong with the loop points (I believe we have seen zero length loop points where the loop start and loop end are the same value have caused an illegal file).

Wavosaur also lets you edit/add/modify loop points. (EDIT: ) Since Montage took out the facility (and MODX also does not have this feature, matching the previous MO series) - you'll need to move what was once a part of Motif into your computer so you can manipulate and inspect your WAV files before importing them into MODX. Once you become adept - it should not add much time to your overall project. The ability to find tools that suit you may be a benefit.

--- aside ---
EDIT - to be technically correct, the "MO" series (MOXF6/8, MOX6/8, MO6/8 ) also did not not have sampling features. So within the product line, nothing was taken away this generation (MODX) with respect to sampling memory. The part about "took out the facility" was referring to the Montage which is the proper product line to compare to the Motif and Kronos presented as examples of instruments which better handle the problematic file(s) you are now working with. I've since edited the original statement.
--- end aside ---

Ok, I'll give it try, here's hoping