Can't burn files to CD

Hi

I'm tring to burn some files to a CD. I insert a blank CD in my drive,
Windows pop me a AutoPlay Window. I choose Burn files to disc.

I give a title and choose the format (Mastered ISO). I click Next. Windows
Explorer ask me to put a blank CD in the X drive. But there is a blank CD in
that drive. I try the same disk on my laptop and it works as it should.

I'm using Windows Vista Beta 2 (5384)

Thanks
Compugab