Failed to make context current

Could you try to add an error handler to see what is going on? Something like this should work:

using System;
using System.Text;
using System.Runtime.InteropServices;
 
class Test
{
	public struct XErrorEvent
	{
		public int type;
		public IntPtr display;     /* Display the event was read from */
		public IntPtr serial;      /* serial number of failed request */
		public byte error_code;    /* error code of failed request */
		public byte request_code;  /* Major op-code of failed request */
		public byte minor_code;    /* Minor op-code of failed request */
		public IntPtr resourceid;  /* resource id */
 
		public override string ToString()
		{
			StringBuilder sb = new StringBuilder(1024);
			XGetErrorText(display, error_code, sb, sb.Length);
			return String.Format("{{Error {0}: {1}}}", error_code.ToString(), sb.ToString());
		}
	}
 
	[DllImport("X11")]
	public extern static IntPtr XSetErrorHandler(XErrorHandler error_handler);
 
	[DllImport("X11")]
	public extern static IntPtr XGetErrorText(IntPtr display, byte code, StringBuilder buffer, int length);
 
	public delegate void XErrorHandler(IntPtr display, ref XErrorEvent error_event);
 
	public static void Main()
	{
		XSetErrorHandler((IntPtr display, ref XErrorEvent error) => Console.WriteLine("Error {0} on display {1}.", error.ToString(), display.ToString()));
	}
}

The error conditions from man glXMakeCurrent:

• BadMatch is generated if drawable was not created with the same X screen and visual as ctx. It is also generated if drawable is None and ctx is not NULL.
• BadAccess is generated if ctx was current to another thread at the time glXMakeCurrent was called.
• GLXBadDrawable is generated if drawable is not a valid GLX drawable.
• GLXBadContext is generated if ctx is not a valid GLX context.
• GLXBadContextState is generated if glXMakeCurrent is executed between the execution of glBegin and the corresponding execution of glEnd.
• GLXBadContextState is also generated if the rendering context current to the calling thread has GL renderer state GL_FEEDBACK or GL_SELECT.
• GLXBadCurrentWindow is generated if there are pending GL commands for the previous context and the current drawable is a window that is no longer valid.
• BadAlloc may be generated if the server has delayed allocation of ancillary buffers until glXMakeCurrent is called, only to find that it has insufficient resources to complete the allocation.

BadMatch error... this rings a bell. I remember encountering this error when a Form had a different visual than the Context bound to it.

As a tangential issue, does a plain Form + GLControl work? Something like the following, maybe:

using System;
using System.Windows.Forms;
using OpenTK;
using OpenTK.Graphics;
 
class Test : Form
{
    public Test()
    {
        SuspendLayout();
        GLControl control = new GLControl();
        control.Dock = DockStyle.Fill;
        control.Paint += (object sender, PaintEventArgs e) => { GL.Clear(ClearBufferMask.ColorBufferBit); control.SwapBuffers(); };
        Controls.Add(control);
        ResumeLayout();
    }
 
    public static void Main()
    {
        Application.Run(new Test());
    }
}

Well, I've corrected the value for the accumulator buffer.
Is there any possibility that the multiple display handles could be causing the BadMatch? This happens because there are two ways of getting the display handle; in Platform/X11/API.cs the static constructor calls XOpenDisplay. Platform/X11/X11GLControl.cs and Platform/Utilities.cs get the display handle via:

Type xplatui = Type.GetType("System.Windows.Forms.XplatUIX11, System.Windows.Forms");
display = (IntPtr)xplatui.GetField("DisplayHandle", System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.NonPublic).GetValue(null);

should these be consistent? This doesn't seem to be a problem on my systems but these are all ATI and Intel video cards; I don't have any nVidia cards to test with.

I still wonder why this failed. On my ati desktop, half of the visuals report a 64bit accumulation buffer, but I haven't checked if you can actually create such a context.

I'm also qurious about what glxinfo reports on nvidia cards.