Xamarin.Forms System.ArgumentException: Illegal characters in path

It had to do with the character length of my solutions folder.

C:\Users\david\Dropbox\Projects\Visual Studio\PriceWatch\PriceWatch\PriceWatchXamarinForms\PriceWatchXamarinForms

(This bloated structure was generated by the IDE, everything after the Visual Studio folder)

I changed it to C:\Projects\PriceWatch\PriceWatchXamarinForms and then it worked.

I our case the reason was that some of our third party dependencies (api assemblies) forced us to set Properties > Android Options > Linking to "Sdk and User Assemblies" instead of "None".

Hope this helps someone... Bad error message.