I am not sure how you are trying to 'import' the LCF file - you don't actually import it as such.
Open the Library manager, press the ADD button and then browse for the LCF file and OK.
That should be it and your objects, doors or windows will be ready for use.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11