Same here, with Xara Photo & Graphic Designer 17.1.0.60742 DL x64 Dec 10 2020... trying to export a 13 m x 2 m banner to PDF produces a "Internal program error 7724.k.xp.gn".
I spent more time trying to reach Magix support than I thought possible - and I could not find any way to contact the company from the support site, except via social media... 🤦♂️
Anyway, I did a few tests and noticed that a simple(r) drawing could be exported to PDF at 13 m x 2 m without any errors. In my case, a large background using a "repeating linear fill" caused the error in question, but changing it to a simple linear fill or solid fill "solved" the issue (of course it didn't, it was just a workaround).