Ok so give it a try with your usb key and told me your results, those commands won't hurt your system or your stick.
In fact :
This will erase all in the stick, and bring us a brand new clear stick
cfdisk /dev/sdb (select type LBA FAT32 may be 0B or 0C, make it bootable )
This will create *ONLY* the partition table with one LBA FAT32 bootable primary partition
mkfs.vfat -F 32 -n SYSRESC /dev/sdb1
This will create the FileSystem FAT32 in the first partirtion
dd if=/usr/lib/syslinux/mbr.bin of=/dev/sdb
This will add the mbr to the top of your stick
Synchronize the drive
Please explain me where you find I'm wrong ...