An assembly with the same simple name has already been imported. Try removing one of the references

I need help.
So I can build and deploy my app on the android. But on iOS I get this error
"An assembly with the same simple name 'Xamarin.Forms.Platform' has already been imported. Try removing one of the references (e.g. 'C:\Microsoft\Xamarin\NuGet\xamarin.forms\4.2.0.709249\lib\Xamarin.iOS10\Xamarin.Forms.Platform.dll') or sign them to enable side-by-side. AssecoSEE.DEM.BA.SPAR.iOS C:\SPAR\DEM_BA_SPAR\AssecoSEE.DEM.BA.SPAR.iOS\CSC"

I tried removing the file mentioned, but I get another error, etc.
Could you guys help me ?