Curretnly I am migrating the aspose cells from 4.8.0.14 into 5.3.0.0 (VB.Net ) and facing issues while saving the work book, also I have checked in your sample code and there is no option to say Open in Excel.
Moreover, please check the documentation of the product for complete details, we spitted the api to move them to different namespaces to make them organized, some api are also renamed and changed too.
check the documents:
Also check and browse the Aspose.Cells for .NET API Reference:
Moreover, if you are building a web application, please use the Aspose.Cells.dll in the net2.0 in /bin directory. For your information, the dll in net3.5_ClientProfile directory is used only for the console application with Net frame client profile as target framework of vs.net. Please check your project, it is possible that your project is referencing this dll. For complete reference, please read the readme.txt file in the bin directory.
Also after looking at your lines of code, your are using obsoleted version of Workbook.Save() method. Please change your code to:
workbook.Save(this.Response, “FileName.xlsx”, ContentDisposition.Attachment, new OoxmlSaveOptions());
Response.End();