Dvd- won't burn

Hi I have a dvd burner. I have no problem burning onto a dvd+RW, but today I tried to burn onto a dvd-rw because my moms dvd player can only read - dvd. At least that's what her directions say. Anyway when I insert a dvd-rw into my dvd burner and use nero it says illegal medium. I bought the dvd burner less then a year ago. I can't remember what brand it is but I downloaded belarc to tell me what it is. It is a BENQ DVD DD DW1620. If anybody can tell me if this will only burn + and not - I can stop trying to figure out why it wont burn dvd-rw's. Thanks.

My burner tells me it is only for + dvd's. i haven't tried with - because on the actual disc it says it can cause damage to the burner. Have you tried to play +'s with the dvd player?

yea, it doesen't read them. That's why I thought it might read -'s. Oh well I guess mommy's out of luck. Thanks