It means .NET 3.5 framework is not enabled on your laptop. Every windows 7 laptop is pre-installed with it.
How to enable:
- Open Control Panel
- Click on ‘Programs’.
- Click “Turn windows feature on or off”.
- Select the checkboxes in “Microsoft .Net Framework 3.5.1” and press OK.
- Close everything & run mHotspot now, it should work fine.
If you are using Windows 8, download and install the .NET 3.5 from here: FileHippo