readonly in gvim windows

Question

I don't know what causes it, but in Windows i use GVim (portable GVim), and need to open some file (that already exist, Vim didn't created it), but it opens it in readonly mode. i need to use w! to write it. I have proper permissions on windows directory, but, this seems like some flag in Vim as it says:

E45: 'readonly' option is set (add ! to override)

i don't want to type w! to save, because Vim is supposed to be portable (run from USB in windows), so it needs to work with foreign files it didn't created. When i create file in Vim, it doesn't complain.

How this work under Windows?

And i already have these flags, but not working:

set noro
set noreadonly
set write

Answer 1

set readonly is set automatically if the target file has READONLY flag set in file system. Make sure you don't accidentally create files with READONLY flag set.