i have noticed an incompatibility trying to use a child domain and wordpress. i think WP is getting confused who actually owns the site especially when trying to upload media files. what i have done thus far to solve the issue is to open up the media directory to world-write & delete.
in other words, i have a structure that looks like this:
_ _ /domain/
_ _ _ _/virtualminChild.com/
_ _ _ _ _ _/public_html/
_ _ _ _ _ _ _ _/wp-content/ (virtualminChild.com's media library is in here)
_ _ /public_html/
_ _ _ __ _/wp-content/ (virtualminParent.com's media library is in here)
i think the wordpress website at virtualminChild.com is maybe expecting a different owner name other than the parent name, but that is just a rough guess.
thank you all very much.