Windows Disk Manager does not work very well with multiple-partition USB flash drives!

 

To re-partition and reformat the USB drive or to remove partitions from the USB drive, use Easeus Home Partition Master free edition. Don't forget to click the 'Apply' button to action the changes.

 

Alternatively, you can use RMPrepUSB, but do not tick the 'Boot as HDD (C: 2PTNS)' box, so that you only get 1 partition.

 

Most new flash drives that are under 32GB, are formatted as a FAT32 'hard disk' with a single partition.