I'm having this issue and I can't seem to give with the solution.

My eMMC is formated as ext3 on /home and ext4 on MyDocs. I have a Kingston microSD card, 16 Gb, 10 class. That card is formated as FAT32, but I can't get my Windows 7 PC to read it.
First, it asked me to format it. Since I've done it previously with gparted, I decided to try with the Windows built-in format tool. And it worked! (with the card emptied) At least until I copied back the files I had from my linux PC. Then again, it didn't even show the disk this time.

What am I missing here? Do you have any problems of this nature?

Yes, I had a similar issue once. It was a few years ago so I do not remember all the details, especially how I got to that situation. So I am not sure if it was exactly the same. But I hope it might help somehow anyway.

The reason behind my problem was that Windows and Linux used different parts of the disc as the FAT table. How could that happen? Memory cards can be formatted in two fundamental ways. Either as a big floppy or as a hard disc. The difference is that the former does not have a partition table but the latter does. Of course, the location of the FAT table is very different in those two cases. I somehow got to the situation where one OS would think my card was partitioned whilst the other OS did not. My case was complicated further by the fact that I had some data on that card not yet backed up on the PC. Unfortunately the PC could not get to it

If you have all your data backed up and do not care about formatting your card again, then I think your best bet is to do just that. Format it again. On the phone, in File Manager. Long press on the card's icon and select Format.

Thanks pichlo. I've everything backed up, so the only thing is getting the thing to work =P

I've tried to format the card from the Maemo file manager, but then (even if I can mount it after that) none of my PC's reads it (Windows or Linux)

My idea is to have the card partitioned in such way that there is a mmcblk1p1 which should be a FAT partition (in this case around 13Gb) and two Linux Swap partitions after that (mmcblk1p2 and p3)

I find it to be trickier than what I thought =/

My emmc and sd card are never exported when I connect phone to pc. I need to execute as a root:
echo /dev/mmcblk1p1 > /sys/devices/platform/musb_hdrc/gadget/gadget-lun0/file

elros34, that worked with the disk empty, but as soon as I copy any file to it from my Linux computer, Windows can't see it anymore.

Delete the partition table and create it again.

I've done that too, and recreated one with a msdos table. Always with Gparted. Maybe the problem is the tool? I'll look for an opensource alternative to use directly from my Windows PC...

After copying the files I mentioned (which makes the partition dissapear under Windows), Gparted says this:

plain floppy: device "/dev/sdc" busy (Resource temporarily unavailable):
Cannot initialize '::'
mlabel: Cannot initialize drive

Even after applying elros34 line.

???

[Edit]

'key. Screwed up my rootfs. Don't know how. I've become to obsesive with this problem. Boot loop. Back to 0.

Sorry for insisting with this, but no one uses his phone as a mass storage device on Windows computers? I changed my card and tried again, but still no luck. The only "real progress" I saw was with the command provided by elros34, but the format of the sdcard is still unrecognized by Windows.

I'm using so I don't get what's your problem is. In n900:
then use e.g. mini tool partition wizard and recreate partitions (first must be fat). Copy files, use safe umount, unplug/plug n900 and everything should be ok if not then once again use: