The error message is "no flash memory module installed or module is unformatted."

You must have a FLASH BOARD installed to load the new Waveforms and Samples. It is the waveforms and sampled audio that get installed on the Flash Board.
Yamaha Flash Board
By comparison the Voice parameters (some of which, as you see, do load) are tiny ...each Voice is less than a couple of kilobytes of data... meanwhile the sampled audio could be measured in megabytes. They can be humongous in comparison...

Say you load a Voice from the CP1 Library... the regular Voice parameters that setup the filter, the envelopes, the effects, etc., etc., amount to about 2KB of data, but one single CP1 piano might be 128MB in size. You will not be able to load any data that points to the Flash Board for its Waveforms and Samples. I’ll explain below. When you separate the Voice parameter data from the Waveform/Samples data you begin to understand.

To really appreciate the difference in size... you may have gotten a gig where you and the band got paid $2,000 (2KB), but I doubt seriously if you ever got a check after the gig for $128,000,000 (128MB) ... so the Voice parameters load — they take only a few seconds to load.

Installing the Sampled audio (the Oscillator) to a Flash Board takes several minutes... some times as much as a cup of coffee or two.

So in the MOXF the structure is Oscillator—> Filter —> Amplitude Generator...
you have LFOs that can modulate the Oscillator for vibrato, the Filter for wah-wah, and the Amplitude for tremolo.
You have two Insert Effects, two System Effects, a Master Effect, a bunch of EQs, etc... all of the parameters add up to about 2K of data IF you remove the Oscillator. (The oscillator is the big DATA).

In a sample-based synth, like the MOXF, the oscillator is responsible for the vibration. It is a high resolution, digital audio recording of the actual instrument sound. The fundamental tone source. It is the BIG KAHUNA. The more samples you have, in general, the more nuance and accurate the emulation of the instrument. In reproducing an acoustic piano... think about sampling each of the 88 notes several times, holding each key until it dies out, then doing it again so that you have 3 Velocity strikes for each key, soft-medium and hard strikes. It’s a lot of data... Then do that for every instrument...
10MB for every minute of stereo record time. The preset Wave ROM of the MOXF is like 741MB of data...

The Chick Corea Mark V (Electric Piano) data is over 400MB of data, very detailed, tons of Velocity layers, all to recreate (very accurately) Chick’s Mark V.

In contrast, an analog synth has an electric circuit (akin to a buzzer or simple door bell circuit) when you complete the electrical circuit it buzzes, you then filter it, amplify it, modulate it with LFOs, etc. Every +1Volt increase the pitch of the buzzer 1 octave.

Flash Boards come in two sizes 512,000,000 Bytes or 1,024,000,000 Bytes (Yes, that’s a billion - Gigabyte)
FL512M or FL1024M

If you don’t have a Flash Board you cannot load those sounds to your MOXF.

Thank you for detailed explanation !
The modules are expensive to me though...