Hello Laura,
This type of error sometimes happens. It could be caused by geometry of the cross section. Can you export the cross section as raw data for this location (MAIN BRANCH', chainage 2000.00 m) and upload the file here? To export a cross-section, select it by double clicking on it's chainage (in the left tree view), than, go to File -> Export Selected Sections -> Export Raw Data... .
Kind regards,
Aurelian