I can not open any older .pdn file. Same error messages as above. I can only open newer .pdn files.   I was semi-sure that those files opened with previous versions of the program within the last year. So I reinstalled 4.2.10 and the older files opened again without issues.   As I kept the program relatively up to date all the time, if it helps, a file that was saved in January 2012 opens, a file that was saved in July 2011 does not open and provides above mentioned erro