Rock Gym Pro requires the .NET library version 4.5 to operate. Please download Microsoft .NET 4.5 directly from Microsoft. You can also download and install .NET 4.5 directly from Rock Gym Pro here.
If you have an older version of Rock Gym Pro, you will need the .NET library version 2 or version 3.5.
For Windows 8, Windows 10 or later, please follow the Windows 8 .NET installation instructions available at Microsoft. For Windows 10, choose the option to enable .NET 3.5 in the control panel.