Cannot record DVDs

[BL7]

A couple of weeks ago I was able to record DVDs with Videostudio7 successfully but now I can't. I keep getting the messages "There is an internal error in the DVD engine" or "Disk space is not enough" eventhough I've tried to record 6MB DVD clips on brand new DVDs that can hold up to 4GB! What could have caused this???
I have a dvd writer/cd writer combo and I am able to record music CDs but not video DVDs.
I'm confused...Please help me...Thanks
BL