Gianmaria,
No, you should not need to create a new catalog. How did you move the files? Outside of Photo Mechanic Plus?
I suggest going into the Catalog Management window and clicking the Reintegrate Forgotten Catalog button for your catalog. If that doesn't correct the issue, contact support directly:
By email: support@camerabits.com
By phone: +1 503.547.2888
Hours: Mon-Fri, 9:00am-5:00pm [PST/PDT]