To reproduce:
GridViewSpreadExport spreadExporter = new GridViewSpreadExport(this.radGridView1);
spreadExporter.RunExport(@"C:\exportedFile.xlsx");

Workaround:
GridViewSpreadExport spreadExporter = new GridViewSpreadExport(this.radGridView1);
spreadExporter.RunExport(@"C:\exportedFile.xlsx", new SpreadExportRenderer());

Alternatively you can set the Copy Local property of the TelerikExport assembly to true.