If you have a large new flash drive that is over 4GB and the file won't fit, it may be that you are trying to store a file larger than 4GB and flash drives usually get formatted in FAT32 so a file larger than 4GB won't transfer despite there being plenty of room for it.
If this is your problem then 'convert' the flash drive to NTFS and it will hold a file up to the size of the flash drive.
To convert to NTFS: (example for a flash drive assigned drive letter F׃)
Start > Run > CMD > Convert F׃ /FS:NTFS > {enter}
Enjoy.