@MarcLasserre_GCS I have the same issue. I created a field that references a Data object, then I deleted the field from everywhere, but am unable to create the field again. It shows the error when trying to create it.
It's almost like there's a field lurking somewhere and you cannot recreate it again even if it's deleted.
@JonC4910 Nope, I looked in the Dev studio as well and deleted any instance found. It still didn't work. I just wasted a few days trying to fix, nothing worked. Finally, I just wiped our the entire instance, created a new instance and started over. It was painful but worked. The lack of support and these things make me skeptical towards using Pega.