That message most likely means that RealPlayer cannot decode the file you're trying to burn onto DVD because of the multiple video streams it contains.
I would advise you to try burning a different file and to make sure RealPlayer can play the file first.
For additional DVD burning troubleshooting tips, please check out the following article:
Please note that Installing the K-Lite codec pack often helps to fix issues related to DVD burning. If you haven't installed it on your PC, you can install it from the link below: