When I launch ChemDraw, I get an error message that the isotopes.txt file could not be found.
First, check to see if the file is on your computer. Do a Find File for ISOTOPES.TXT. If it was not installed or is missing for some reason, reinstall ChemDraw.
Next, it could be that you moved the chemdraw.exe program to a different location, like your desktop. If you move the ChemDraw program from the original location, it won't be able to find the ISOTOPES.TXT file which needs to see when it launches. Instead of moving the ChemDraw application, make a shortcut of the program, and then move the shortcut whereever you like.