Toad puts a series of random characters at the beginning of text files. They aren’t visible on most text editors, including Toad itself, but are visible in some other editors, i.e. using gVim on Windows.
This isn't always a problem. It seem to appear randomly. It causes SQL Plus to fail when trying to run.
"Newline format" is set to UNIX under View | Options | Oracle | General. It's only newline characters that causes issues so only appear when entering or attempting to remove a new line from the top of the file.
Change the setting to "Windows Style" under Newline format setting in View | Options | Oracle | General.
Another similar issue to refer to:
SOL89675 Saving a script via Editor window results in non-readable SQL or TXT file.