1] Run CHKDSK. Using CHKDSK is also one solution that is proven to be effective to fix the Invalid MS-DOS Function issue.. To run CHKDSK, do the following: Press the Windows key + R.

The system file is not suitable for running MS-DOS and Microsoft Windows applications. Choose ‘Close” to terminate the application.” “16-bit MS-DOS Subsystem ...

MS-DOS File System is the older FAT filesystem used with MS-DOS and Windows. Note that you can't have files of 4GB or bigger on a FAT volume. UNIX File System (UFS) is exactly what the name suggests.