Ok, that is why I always recommend to use UUI and also from Windows so the result is "guaranteed". With other installers there might always be some headache. I had same problem with using wine, it did not detect my USB.
"But dont delete it, you will have to use it, to do things that we should be able to do in linux"
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Now I tried to use the Startup Disk Greator. I made a Zorin 8 Lite installation to a 8 Gb San Disk Cruzer Blade USB Drive. I made there also 4Gb persistent file there. I booted up in my HP 530 laptop without any problems. As I said it will boot up and run whatsoever which is "something" software. Untill now it seems to work ok. Sorry that I can not help any other way. This was the first installation using that installer so no further experience until now.
I have looked the content of the USB drives having the same os. installed. There are differencies in the setups of the folders and files and their naming. I believe that some boot processes in different BIOSes simply does not manage to boot from all versions of USB installations like my HP530 does and that is the reason to boot failures. So only, or at least simplest way to overcome this is to find an installer that makes the file setup working also in some more stubborn computer.
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Regarding the naming of folders and files.
If you used UII so there should be following folders and files in your USB:
isolinux (folder) including
isolinux.bin
isolinux.cfg
UUI (folder) including
ldlinux.sys
syslinux.cfg
These folders, files and naming is done automatically to USB by the installation software when using UUI.
I tried to use the
"Startup Disk Creator" installation software, installed from software center. It is a Linux USB installer to make a bootable drive. It worked well. Booted in my HP 530 laptop just fine. In that installation the folders are as follows.
ldlinux.sys (file)
syslinux (folder) including
isolinux.bin
syslinux.cfg
In the UNetbootin the folders are as follows:
isolinux (folder) including
isolinux.bin
isolinux.cfg
Same as in UII but not having a UII Folder.
So depending on the installer used there are somehow different setups with the folders, files and names.
My suggestion is here that if you have problems with booting, so the setup in UUI works best not to stack in some booting error. There is machines like my HP 530 that don't mind so much of the setup and naming, all works. However there are some more stubborn ones that works only when folders, file setups and names are in a specific way arranged. The question is how capable the booting proses in the BIOS is to handle different styles of installations.
btw. you never told what was your computer specs ?