Bootcamp - "The selected drive has been ejected" error

Hello,

I have MacOs Majove 10.14.5 (18F132) installed on my MacBook Pro (15-inch, Mid 2012).

As of now (Wed 19th, 2019) my system does not request any OS updates. I have more than

50 GB space in my drive partition where MacOs is installed and in another partition

I have Windows 10 installed.

I recently had to do a fresh installation of my Windows 10 and started to use Boot Camp

Assistant to create a Windows support drivers usb. I used two different USB flash disks with

different manufacturers but each time driver download finishes and I guess copying of files

to the USB disk starts and about 3 minutes remaining to complete the whole thing,

I get this error:

The Windows support software could not be saved to the selected drive.

The selected drive has been ejected.

Well this is very strange because it was never ejected or used during all 8 attempts. I formatted

the drive to MS-DOS FAT with MBR using Disk Utility as recommended. Bootcamp also doesn't

allow other formats when I tried for test purposes. But I get the same error each time no matter

of which USB flash disk I use (I have tested 2 disks, one 16GB, other 128GB capacities).

Bootcamp never warns me about an issue with the two drives I tested. Drive utility was closed

also to not have any locking issues so it is not the matter I believe. I couldn't find anyone having

exactly the same issue with me on my google searches.

Looking forward for your assistance.

PS: Disk Utility formats my usb drives in MSDOS FAT 32, not FAT 16 no matter what I do even I chose

each time FAT, not ExFAT.

Thank you,

Ozan.