Hi Felique,
The assemblies referred to the sample is not available in the mentioned location, and so the error is shown. We request you to refer the assemblies Syncfusion.XlsIO.Portable.dll and Syncfusion.Compression.Portable.dll to the sample to resolve this error.
We also request you to upgrade to our latest version (15.1.0.33) of Essential Studio which has more bug fixes and enhancements which is available for download under the following link.
The assemblies will be available under the following location in your machine.
$system drive: \ Program Files\Syncfusion\Essential Studio\$Version # \Xamarin\lib\pcl
Eg : $system drive:\Program Files (x86)\Syncfusion\Essential Studio\15.1.0.33\Xamarin\lib\pcl
Please let us know if you have any concerns.
Regards,
Abirami.