Can't get firmware upgrade for refurbished Sansa m240

I have several Sansa m240 players. Two of them have firmwware version 4.1.07a. They work fine with everything I need to do.

I have two other Sansa m240 players, just purchased as refurbished units. When connected to my computer (a Mac), the new ones report 0 MB free (unlike the ones above, which report the correct size). The new ones have firmware 1.3.0a. Using a PC, I have downloaded the Sansa firmware updater, and it says firmware updates aren’t available. I also tried the m-series dedicated firmware elsewhere on SanDisk’s site. It won’t upgrade the firmware either.

The newly purchased m240 units simply refuse to work using the exact same configuration as the prior ones, so the firmware seems like the only difference.

What can be done to upgrade these new players?

For firmware specific and all other questions: Email support@sandisk.com