Thanks for the screenshot, and @RaveyDavey for the translation.
The error message suggests that, if you are using the Plus or Premium version, you have not installed all the extra content which includes the extra tracks - Store tab, click the gear and select Download all purchased content... This must be done - upgrading to the latest version is in effect a new install.
I have purchased MMM 19 and it should let me have unlimited tracks
Purchasing the program is only the first step. After registration you then have to download the content you want from the store. If you don't then all you have is the same version as the free version.