Hi and welcome to the forum
FAT32 has some limitations. Even if you copied 22GB of files, I guess that none of these files was more than 1 GB in size. 22GB was the total dimension of the folder, but the FAT32 limit is in the size of a single file, not the sum of all files.
To copy a single 4GB file on a FAT32 drive is not possible.
You can convert the drive into NTFS (it can be done with the DOS command "convert" without loosing any data) or you can split the ISO into chunks with WinRAR or 7-zip