I have evaluated your scenario/ case a bit using your template XLS file, I still could not find the issue. Well, Babar is right, your worksheet is actually protected, so you cannot insert any value into the cells in the worksheet. Anyways, I just opened and re-saved your template file by Aspose.Cells APIs. I can select items in the drop down fine (as I can do this in the template file, moreover, we cannot select items in some other drop downs as the worksheet is password protected, so it cannot be done in the output file too.) in the output file, see the screen shot here:
I used the following sample code with your template file (I have attached the output file for your reference here):
Aspose.Cells.License license = new Aspose.Cells.License();
Workbook workbook = new Workbook(“e:\test2\SAP_Enabler_New.xls”);
If you still have any issue, please provide more details and create a simple sample console application (you may zip it prior attaching here) with our latest Aspose.Cells for .NET version v8.5.2.x to reproduce the issue on our end, we will check it soon.