Thank you for your post.
As you mentioned, for Windows 7, .NET Framework 3.5 with SP1 is shipped with it as one of OS component.
For .NET Framework 3.5 with SP1, it includes .NET 2.0 with SP2 and .NET 3.0 with SP2 as prerequisite.
This means, you have the .NET Framework 2.0 SP2, 3.0 SP2 and 3.5 SP1
plus a few post 3.5 SP1 bug fixes on Windows 7. They are OS components
. We don't need to manually install it.
For your concern, could you please check whether this scenario will happen if you turn on the windows feature of .NET Framework 3.5.1 before you try to install the installer
using Installshield 2009 Pro?
Please go to Control Panel -> Programs and Features -> Turn Windows features on or off -> Check the box next to Microsoft .NET Framework 3.5.1.
After the windows feature has been turned on, it means that .NET Framework 3.5 with SP1 is well installed
on Windows 7.
If the problem still exists, could you please help me to check whether this scenario will happen on other Windows 7 machine?
This would be helpful to eliminate some possible cause of this machine specific.
For more information on this warning
message, please check: http://msdn.microsoft.com/en-us/library/dd371711%28VS.85%29.aspx
Hope this helps! If you have any concern, please feel free to let me know.