This happend to me recently . Had two projects out of action for a couple of weeks. Graphisoft have recognized this as a bug and these are the instructions I got.
By the way are you using Cadimage tools.
Graphisoft have acknowledged a fault and will be issuing a new hotfix next week, in the meantime this is what I suggest:
1. repair your Archicad install from DVD and download and reapply hotfix 1040 from
http://www.graphisoft.com/support/archicad/downloads/ReleaseNotes/AC11-1033to1040-FixedBugsList.html
2. close all Archicad windows except the 2D plan window prior to saving the file*
3. you cannot paste data into a section window with hotfix 1086 installed.
PS - a problem occurs when you save Archicad with a section window active. I urge all clients to close ALL windows except 2D plan window when saving and closing their Archicad projects.
Richard.
Richard Wilden Design. Ltd
Dunedin, New Zealand.
Imac 27" i9 3.6GHz; 32GB Ram Mac OS 11.3
Archicad V23:V24