I've been having a awful time attempting to burn to a existing rewriteable disk that already has both data and video on it. I have tried both Creator Classic and My DVD with no luck. I'm using Creator 9. Please advise!!!

I'd advise you to post the correct name so we can help. Do you have Creator 2009 or Easy Media Creator 9 or an OEM version of 9 that came on your computer. They are different.

How did you make the disc in the first place? Sessions as a data disc? With Creator Classic you have to import the previous session (misnomer) and then add the new information as a new session. If you made it another way, please tell us how. MyDVD will not do it.

What OS are you running?

Just because a DVD is rewritable does not mean you can add new files at any time. It all depends on how the original data was burned to the disc. As sknis has posted you will have to tell us what program was used, how it was done. myDVD can never be used to add files to an already burned DVD.