Encountered the same problem.
Usually occurs when i have been in a Windows program (Explorer, Excel, Word etc) where you can scroll up and down, then clicked back into ArchiCAD.
Usually fixed by going back into Explorer and scrolling up and down and maybe clicking on a file or folder (any file or folder will do) then going back into ArchiCAD to find the scroll has started working again.
I have not found a reason why switching between programs causes this little hiccup.
If that doesn't fix it i close and restart ArchiCAD and that fix's it.
Cheers
Stu