Are you sure your USB drive is mounted as /mnt/Retro Drive ? Is the user that's running EmulationStation (RetroPie installation user) able to access the driver and its contents ?

@kaz69 No, only one OS boots at a time. Nothing additional is running in the background from the other installations. Not sure if PINN asks or allows you to set the partition sizes but obviously it would be handy to have larger partitions for those OSes that need it.

I am back, well rested and ready to go on what could be my final attempt before I give up.

9:52pm
-What I did different, formatted RP Micro SD card to FAT32 (32gb card) previously was ntfs, I don't even know if it matters. I'm unplugging my ethernet wire. I'm transferring the rom folders that screwed it up in the first place, first.

Transferring over 3 'problem' folders first, plugging external into pi. works, transferring over every rom folder but about 4 now.

10:26pm
3. mostly all rom folders are transferred, about to test it now.
4. boost file system error as seen above..... i dont know what to do.

@Chien-Dinh it says drive is too big.

@Caustra if you are talking about dvd rom drives and stuff then you would at the minimum mount the drive. You need to mount a dvd drive everytime you put a disk in it. To have it mount on startup you need to put a command in startup to do so. You need to open /media/ and add a folder called cdrom. Then you need to tell the system to mount sr0 to that folder. I can tell you how to do all that but because it does not show up as a usb i dont think it will work.

Because it's close to what I'm using and I can't find help anywhere :(