DVD Burner - Why is it that...

Why is it that my DVD burner is NOT recognizing a blank DVD-R? It will recognize a blank CD of any sort, and a blank DVD+R, but not the DVD-R. It also plays both audio and video perfectly.

I need to burn videos edited with Pinnacle Studio Plus Version 11, with specific instruction to burn to a DVD-R. Problem is, when I get to the point to burn and insert the DVD-R, it ejects and tells me to insert a DVD. It does, however; recognize the DVD+R when inserted. It's honestly driving me batty. I have uninstalled and reinstalled the driver and it did nothing, which I figured wouldn't help since everything else is immediately recognized when inserted but the DVD-R. HELP! Anyone got any ideas? I'm losing work - and my mind - by the minute.

The device is an HP DVD Writer 300n 1.25.

Also, since I DON'T know - what is the difference between a DVD-R and a DVD+R? Would it matter too terribly if I used the DVD+R, or is there a "good" reason for my employer to want only the DVD-R?

I thank you guys in advance - I'm dying over here...

 

There is not much difference between the two formats. The DVD-R can hold a slightly more amount of data.
http://en.wikipedia.org/wiki/DVD-R
http://en.wikipedia.org/wiki/DVD+R
The main thing is: Is your burner compatible with both medias?