I'm assuming you have a MOXF 6

https://yamahasynth.com/learn/moxf/moxf-flash-memory

I just recently purchased a MOFX6 from Sweetwater. It came with a usb drive with sounds. Do I need a flash module to upload sounds? I tried to upload per the instructions in the manual but I get the error message “No Flash Memory Module Installed or module is unformatted”. Thanks

You need a Flash Board if the sounds you are attempting to load contain new Waveforms and Samples.
What that means is... the MOXF is based on a technology called AWM2 - Basically, Yamaha’s proprietary method of storing and retrieving sample data for synthesis.

The MOXF comes with 3,947 Preset Waveforms... the sounds, which are called “Voices”, are made from these Waveforms.
There are 9 Banks of 128 Preset Normal Voices and 72 Preset Drum Kits.

You build synth sounds using Oscillators (sound source) > Filters (control timbre/tone) > Amplitude Generator (control loudness).
The Oscillator (sound source) can be any of the 3,977 Factory Waveforms... you can build an unlimited number of sounds using just these factory waveforms. There are some 741MB of samples that make up the 3,977 Waveform

New Waveforms can be loaded only to a MOXF that has a Flash Memory Expansion board installed.
Not all Files provide new Waveforms data...
Many Library files for the MOXF will utilize the onboard Waveform... some Library files add new Samples to your synth, by installing the new Waveforms to your Flash Board.

You can verify if your MOXF has a Flash Board as follows:
Press [FILE]
Press [F6] FLASH

The screen will report on the Board, if any.
FLASH BOARDS - FL512M or FL1024M

Thanks for explaining that. I think my Sweetwater rep may have been confused on how that works.