I have a similar issue, but a bit more nuanced. I downloaded v3 today and was setting up. When I was initially setting up, I had pilot2atc v2 running on another desktop importing taxiways and gates. When I got to the data mnt portion in the Quick Start First Flight walkthrough, I initially pathed to the pilot2atc data folder but then thought better of it given that I v2.0 was still active and busy, and not wanting to screw it up. I did the rest of my setup with voices and stuff and quit out. Later when pilot2atc 2.0 was done, I closed that and launched v3. When I launch now, I get a DataMgr.Init Error with the app saying "Loading" behind it. I OK that dialog and it finishes loading. If I now go to the Settings->Utilities and press the Data Mnt button, I get a CTD with no dialogs or errors. I came to this thread and did the above steps regarding the Navigraph FMS Data Manager and all of that went fine, but I'm still getting the same CTD. I tried just renaming my pilot2ATC 2.0 folder temporarily in case it was a config thing where it had a path it was evaluating, but no luck. I assuming its just a bad config issue or something like that where it got into a weird state, so if this comes down to removing a settings xml, if we can be surgical about it, it would help me save all the voice work I did (deleting all of the AWS voices I had that I didn't want to use was a pain). Here's my log and a screenshot. Let me know if you'd prefer it in another form:
https://drive.google.com/drive/folders/1HM0IqmZ6z-AF7R8T6M5okywAEvUmH83C?usp=sharing