I have done the registration manually using regsvr32 and it worked fine.

But I went back to my installation package to see what was wrong.
In this package I have changed the "Registration Type" property for the DLL to "Extract COM information" instead of "Self-registration" as recommended in the VFP sample "Walkthrough: Creating a Visual Foxpro application setup program using InstallShield" provided with VFP help. And in this sample doing this was highly recommended.

So, after changing it back to "Self-registration" and building a new setup program; everything worked fine.

Thank you again.