Problems importing PSE Catalogue into LRC

Hi - I am trying to import a catalogue from PSE 2022 into the newest LRC version. Step 1 and 2 run smoothly, but then in step ("Zusammenfügen / Merge"), the import stops at about 10% and I get an error message saying that the catalogue could not be imported because of an "unknown error". I am using time machine, but have disconnected my external HDD during the import? I have a MacStudio with a new M1 Max chip and MacOS Ventura. Any idea what to do?