Error is received when click on button. Reproduced randomly on different machines.

Since 2025 Q2 you'll get this error message when you try to open a flyout on a control that is not a Form. This does not happen with 2025 Q1.

Might be related: https://feedback.telerik.com/winforms/1688619-radform-clientsize-on-inherited-radform-is-broken

However, this time I have no patch / workaround. I have not the time to investigage deeper at the moment, so update to Q2 not possible for me at the moment.

 This issue starts happening as of Q2 (2025.2.520) version.

Workaround: override SetClientSizeCore() inside of inherited RadForm

public partial class RadForm2 : RadForm1
{
    protected override void SetClientSizeCore(int x, int y)
    {
        base.SetClientSizeCore(x, y);

        if ((!this.IsLoaded || !this.IsHandleCreated) &&
            this.IsInitialized)
        {
            MethodInfo mi = typeof(Form).GetMethod("SetClientSizeCore", BindingFlags.NonPublic | BindingFlags.Instance);
            if (mi != null)
            {
                IntPtr ptr = mi.MethodHandle.GetFunctionPointer();
                Action<int, int> baseSetClientSizeCore = (Action<int, int>)Activator.CreateInstance(
                    typeof(Action<int, int>), this, ptr);

                baseSetClientSizeCore.Invoke(x, y);
            }
        }
    }
}

Add a call to "OnImageLoaded" to "RadPictureBoxelement.PasteImage()" method or create an event like "ImagePasted" ot be able to tract an image change at this point.

For me I solved this via an Harmony patch that adds a call to OnImageLoaded() on PasteImage()  long time ago. Not really elegant, but I'm a noob in patching with Harmony.

Just want to leave it here for anyone that want ot use this solution too or for Telerik to implement a native way to expose an image change via PasteImage.

[HarmonyPatch(typeof(RadPictureBoxElement))]
[HarmonyPatch("PasteImage")]
public class RadPictureBoxElement_PasteImageFixes
{
    private static readonly Dictionary<RadPictureBoxElement, Image> images = [];

    public static void Prefix(object __instance)
    {
        if (__instance is RadPictureBoxElement pb)
        {
            // Remember our image
            images.Remove(pb);
            images.Add(pb, pb.Image);
        }
    }

    public static void Postfix(object __instance)
    {
        if (__instance is RadPictureBoxElement pb && images.TryGetValue(pb, out var image) && pb.Image != image)
        {
            // Remove first to avoid conflicts on error
            images.Remove(pb);

            // Call "OnImageLoaded"
            var method = typeof(RadPictureBoxElement).GetMethod("OnImageLoaded", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
            method.Invoke(pb, null);
        }
    }
}

Steps to recreate:

• click on the button on the top row
• press the down key on the keyboard
• Press Space key to select new button, the button on the top row is clicked

When trying to open the QuickStart solution from 

C:\Program Files (x86)\Progress\Telerik UI for WinForms 2025 Q1\Examples

installation folder, the following error appears:

Visual Studio 2022 crashes when working with a solution containing two WinForms projects:

• Project 1: WinForms (.NET 9) with Telerik
• Project 2: WinForms (.NET 6) without Telerik

Steps to Reproduce:

1. Create a new solution in Visual Studio 2022.
2. Add two WinForms projects:
   • Project 1: WinForms (.NET 9) with Telerik
   • Project 2: WinForms (.NET 6) without Telerik
3. Open the WinForms designer for a form in Project 1 (Telerik, .NET 9).
4. Without closing the designer, open the WinForms designer for a form in Project 2 (.NET 6, no Telerik).
5. Switch to the code view of the form in Project 2.
6. Switch back to the WinForms designer in Project 2.

Expected Result:
Visual Studio should smoothly switch between code and designer views without issues.

Actual Result:
Visual Studio freezes and crashes after switching back to the WinForms designer in Project 2.

Environment:

• Visual Studio 2022
• Windows Version: (Windows 11 x64)
• Telerik WinForms Version: (2025.1.211)

Additional Notes:

• The issue seems to be related to handling different .NET versions and Telerik components in the same solution.
• The crash occurs consistently when following the steps above.
• No explicit error messages are shown before Visual Studio closes.

When the RadPropertyGrid is in group scenario and we expand more property items, the scroll value is incorrect. 

Workaround: set UseCompatibleTextRendering to true.