I downloaded the hardware files for a Nordic Development kit. https://www.nordicsemi.com/Products/Development-hardware/nRF9160-DK/Download?lang=en#infotabs, the text on the error says:
"""
pca10090_sheet1_connections.SchDoc
Imported from Altium ASCII
Cannot import Altium ASCII file because it isn’t the correct format.
"""
Need more help, and Learn More buttons do nothing.
The project imports into Kicad just fine.