we were trying to open a MaxQuant search (version 188.8.131.52) with the new modifications Iodination (Y) with the "Import DDA Peptide search" from skyline (version 20.2). Before that we saved the new modifications.local.xml and modifications.xml into the same folder, where the msms.txt file is located. Nevertheless it still gives us the added error.
With chlorination (Y) we got a corresponding error.
If we try to open a MaxQuant search for only oxidations (M) skyline works fine.
I hope you can help us with that problem,