You must run it from the MPI folder because it will use MPI to make a .imgPTN file.
Split_WinISO.exe can also re-make a new .ISO file and convert the large >4GB Install.wim or Install.ESD file(s) into smaller files for you.
It has been written to interface with the Easy2Boot MPI Tool Kit (if it is placed in the MPI folder).
In addition to splitting large .wim/.esd files, it can also add the missing Windows 7 EFI boot file and modify the boot.wim file for automating Windows Setup using XML files (see here for more details).
Load the ISO file and click on CONVERT if the install file is larger than 4GB.
Use the MPI button if you do not want to split the install.wim file.
Errror 3 - check the path and filename does not contain any weird characters (like ( or & or =, etc.) - try renaming it. Use 7Zip to open the ISO file and then double-click on the install.esd or install.wim file inside the ISO - 7Zip should list the files inside the .wim\.esd file - if you get an error then suspect that the ISO is corrupt. Check the MD5\CRC32 hash of the ISO - try a different ISO.
Make sure your C: drive (or whatever drive Windows uses for temporary storage) and the drive where the ISO is stored has plenty of free space (at least twice the size of the ISO as free space).