Error "Attempting to insert an item that is already part of a collection"

After aligning two big word documents I cannot save it in SDLXLIFF. It gives me the error "Attempting to insert an item that is already part of a collection". It only allows to save it in SDLalign, so I cannot import it in my translation memory.

What can I do?

The files were converted from PDF, but the conversion was quite cleaned.

Thank you for your help!

 

Diana