Conversion problem

Conversion of work from V-3.6 to V-4:
1. Upon opening a work sheet, you are told that the file will be upgraded from v-3.6 to v-4.
2. After the program conversion the new file has a discrepancy, meaning that the note ties are converted to slurs automatically.
3. Upon midi playback you hear the individual notes instead of the tied notes,
4. Upon close examination you see that the ties have become slurs instead of ties.
5. This conversion action requires the author to go back and re-do the ties after deleting the slurs.
6. Which brings my question, why do we need to use slurs when we can just hear the individual notes played?
7. And how do we insert the slurs at all?