I am trying to assign section properties from within the STAAD.Pro Physical Modeler. The Assign Section dialog box comes up but I do not see any profiles in the tables. What could be causing this ?

This error is most likely related to Microsoft .NET Framework not being installed in the machine. So for anyone experiencing the issue, a first check would be to ensure that the .NET Framework 4.6.1 or higher is installed. 

In addition, one should ensure that the Bentley Property Catalog Service should be running. To check that, please follow the steps below

1. Log in as the administrator.
2. Right click on the Task Bar and select Task Manager.
3. Go to the Services tab. Select the Bentley Property Catalog Service, as shown in the picture below.
4. Right click on it and choose Start.

After the above requirements are met, the issue should be resolved. 

In case there are still issues, please try to launch the Structural Property Catalog Management studio from the location indicated below

"C:\Program Files (x86)\Bentley\Engineering\SPC Server v8i SS4\Tools\Bentley.Structural.PropertyCatalog.ManagementStudio.exe"

Check if this catalog management application launches and if the profiles are visible as shown next

If the initial steps described above, did not resolve the issue, one would most likely get errors during launching of the catalog management studio and the error should indicate if any pre requisite is missing. Please contact your system administrator and get those necessary files installed. If that does not resolve the issue, please contact Bentley Technical Support by creating a service request. 

Details on how to create a service request is available in the wiki below

https://communities.bentley.com/communities/other_communities/sign-in_assistance_and_web_services/w/wiki/47172/how-to-create-a-new-service-request-online