Windows Store package upload error for WP 8.0

Hello,

I am trying to deploy a Windows Phone 8.0 Silverlight app to the app store (unfortunately we have the requirements to support this old version of WP).

I am getting this error when trying to upload the .xap package:

"Package acceptance validation error: We don’t allow embedded EXEs. Remove the roslyn\csc.exe embedded EXEs and then try again.
Package acceptance validation error: We don’t allow embedded EXEs. Remove the roslyn\csi.exe embedded EXEs and then try again.
Package acceptance validation error: We don’t allow embedded EXEs. Remove the roslyn\vbc.exe embedded EXEs and then try again.
Package acceptance validation error: We don’t allow embedded EXEs. Remove the roslyn\VBCSCompiler.exe embedded EXEs and then try again."

Please note that the app is built with Xamarin framework, using Xamarin Forms.

Does anyone know what's going on?

Thanks for your help,
Roland