I can't categorically state that your burning problem is due to the small amount of RAM in your computer, but you are asking for endless troubles trying to work with Magix programs on that PC. You need to upgrade to a minimum of 2 Gigs RAM before trying to do anything in most Magix programs.
According to the Magix website, the current version of Rescue your Videotapes requires a minimum of 512 mb RAM. Frankly, it surprises me that they indicate a minimum that small, but in any case, you have half of that.
I'm also guessing that a computer with only 256 mb RAM is also very old, which means the drivers for your graphics card and your DVD burner may not be supported any more. There could be a number of problems causing the failure.
If you were burning to your HDD instead of your burner, you may have run out of HDD space.
I recommend you upgrade your RAM anyway, 256 just isn't realistic any more. If you can, get a more current computer with up-to-date components (especially graphics).
I'm sure you didn't want to be told that, but, there it is.