Yeah found the problem. I uploaded it to my Dropbox folder in order to make it accessible from everywhere but when you run it from Dropbox folder it locks itself out because Dropbox client tries to sync it as the temp files are being created each time I try to create an installation USB. So the solution is to copy it to somewhere local and run it from there. I see the log message saying that it's locked I knew something was locking it but unlocker wasn't showing anything and fresh restart didn't work either but then I thought about the Dropbox client and boom! It was the reason.
So if you back it up on Dropbox, don't run it from there, just copy it to a local temp folder
Thanks @The Finder