Migrating from Ableton 9 to 10 - BUG? - "The file "xxxx" could not be decoded using QTKit (error code 0)"

[Nilzie]

Dear Abletoners - I'm trying to migrate from 9 to 10 - and am running into a big problem:

When trying to open my working document, that I use during our concerts to play back a number of files, both audio and video, and now when trying to open my live document in Ableton 10 (I've been working inside Ableton 9 up til now), Ableton can't load the document, I get the same error message:

The file "xxxx" could not be decoded using QTKit (error code 0)

Please advice

My thoughts:
- does this happen because my Ableton 9 document was saved with the 32-bit configuration?
- could I use another solution than the QT-kit? (https://developer.apple.com/documentation/qtkit)

Best wishes

/ Nils

Mac OS 10.12 (Sierra)
Hardware Configuration
Macbook Pro, Late 2016
2,9 GHz Intel Core i5
16 GB 2133 MHz LPDDR3