one thing I've noticed very often with flash drives and sometimes with external HDDs is that windows doesn't need a partition table, you can mkfs the "root" device (the equivalent of "mkfs /dev/sda" rather than "mkfs /dev/sda1"). windows will cheerfully mount this, but linux automounters might not.

so, check the disk has a partition table using "fdisk -l" on a full linux box.

in fact, my nokia e65 will refuse to work with the microSD card partitioned, it will ask to erase it and write a partition-less file system!