So I've had a few games recently which, quite late in the game, I suddenly lose the ability to create webway links between my building. The icon (hotkey d I think) is greyed out and when I hover over it, its says something like "relocation not available", which is odd, as it is not the relocation option the the button uses, it is the link button. Relocation (hotkey z) works fine.
My buildings had taken some dmg but the option was still greyed out when I repaired them (unless I missed a building). Also, its only seems to happen quite late in the game. But only sometimes.