Oh, interesting. That would mean he's not where he should be (he should only be gone at night), and the game is trying to run his dialog without him being there. We fixed this issue once before, but it seems something else has happened that we'll have to check out.
Viewing post in Bug Report Full Release 1.1.0.0 - Bathhouse Update
Yeah Garret wasn't there at dawn/day/dusk after saving Warrick. Basically I did 5 nodes > Garret sparing cutscene > completed saving Warrick > Warrick was waiting for me to leave for Dragon Roost > I refused to check if I missed anything > Went to Garret's place and no Garret and interacted with his house > error message appeared.