When clicking on a dropdown menu it says No Data to Display when there is data for the dropdown menu.
The user doesn't have permissions to view the data in the dropdown menu.
Open the administration tool.
Locate the end user and expand their roles and groups.
Locate the role or group that should have permission to view this data. Typically it will be "portalEndUser" role.
Right click on the role and choose Privileges.
Next locate where the drop down menu is in the sections. For example you could look under Modules->Incident Management->Non-Process Related Objects.
You could also look in Modules->Incident Management->Process Related Objects->Incident
Make sure the role has read permissions to this object.
After this the users will be able to view the data in the dropdown menu.