The program does calculate what will fit onto one disc before rendering, which is basically just dependent on the duration of your movie and the encoding bit rate in the MPEG-2 encoder. Sometimes, the calculation might just be slightly off, especially if you have very large menus. That's why it might be a good idea to lower the MPEG-2 encoder bit rate a little further below what the program suggest if you encounter any problems with incorrect space calculation. However, that is not the problem here. As you wrote, you specifically chose not to reduce the quality/bit rate, but went with the option to split the project. The MPEG encoding process is a little more than just a mere "preparation" for burning. This will always take a while.

There have already been plenty of questions and answers regarding CD or DVD burning problems in Magix programs here. You might want have a look at some of the older posts and try the search function, as I'm sure you can bring up some more extensive replies. Here are the most important points in a nutshell:

* Make sure your burn routines are up-to-date. That is the software interface Magix uses to burn in the programs. It's updated on a regular basis to implement improvements and support more burners. You can always find the most recent update on the Magix support website in the downloads section under "Tools".

* Pretty much one of the first steps in any burn troubleshooting should always be the testing of other types and makes of CD/DVD blanks. Not all blanks work well with all optical drives. Make sure your drive is generally supporting the type of blank you're going to us as well.

* Up-to-date firmware for your burner might also be a good idea. If a newer version is available, you'd find this through the website of the manufacturer.

* Sometimes, other software can interfere with the burning process in the Magix program. This is especially true for other software related to optical drives and disc-authoring. So, you might want to shut down other applications and background tasks that are not essential when working with the Magix software. Some of these, you might actually want to disable in the "Startup" tab of your "msconfig" Windows system configuration utility, so they don't even start up when booting the system. But it doesn't stop at actual applications. Some programs install really intrusive filter drivers that will alter and influence the communication chain between applications and drives and require the application that brought them into the system to be uninstalled to get rid of these filter drivers again. (And sometimes even that doesn't do the trick.)

On that same token, you might also want to unplug external devices (connected via USB) that you don't really need for the time of working and burning in the Magix program.

I think this covers the most important aspects and hope it helps.