Crossword Construction Kit 4 should not be installed in the same folder as previous versions of Crossword Construction Kit. By default, Crossword Construction Kit v 4.0 is installed in a different folder than Crossword Construction Kit v 3.x.

Crossword Construction Kit 4 will read puzzle files created by Crossword Construction Kit v 3.x. However, when it is opened by Crossword Construction Kit 4, the file will be converted to the Crossword Construction Kit 4 format. Once converted, Crossword Construction Kit v 3.x will no longer be able to open and read the file.
Note: We recommend that you copy (back up) your puzzle file(s) before opening them in Crossword Construction Kit 4.