Abruptly files that have been edited on a Mac are corrupting when opened on PC and a save is attempted - often crashing InDesign repeatedly. Can normally eventually save a copy to 'Downloads' - rather than the shared Dropbox folder and then overwrite but tends to take several restarts and recovery attemps / saving as idml. Gives a variety of error messages - sometimes error 2, sometimes unable to do this process, some times tried to save but couldn't... any ideas?!