The device is formatted as FAT32 and the largest file size FAT32 can handle is 4GB. You have two options, 1. convert the format to NTFS or 2. split your 4GB file into smaller pieces.
If you can’t convert the format to NTFS but rather can only do a reformat to NTFS then be sure to backup all the files on the drive including the hidden U3 system folder and restore them after you do the reformat. If you don’t backup the hidden system folder you will loose all your U3 apps since SanDisk doesn’t have them online any longer.
