The object is currently in use elswehere

Below is a snippit of code that is supposed to capture the image of a
visible window, and copy it to a picturebox control on my form. My
picturebox control is on a tab in a page control. Everything seems to work
fine except when I select the page that the picturebox is on to make it
visible, I get a System.InvalidOperationException in system.drawing.dll 'The
object is currently in use elsewhere'. Any ideas?

this.PictureBox1.Image = CaptureWindow(hwndWindowToCapture)

public static System.Drawing.Bitmap CaptureWindow(IntPtr
hWndWindowToCapture)
{
RECT pRect;
pRect.iLeft = 0;
pRect.iRight = 0;
pRect.iBottom = 0;
pRect.iTop = 0;

int iRetVal = User32.GetWindowRect(hWndWindowToCapture, ref pRect);

int iWidth = pRect.iRight - pRect.iLeft;
int iHeight = pRect.iBottom - pRect.iTop;

POINTAPI pPoint;
pPoint.iY = pRect.iTop;
pPoint.iX = pRect.iLeft;

iRetVal = User32.ScreenToClient(hWndWindowToCapture, ref pPoint);

pRect.iLeft = pPoint.iX;
pRect.iTop = pPoint.iY;

System.Drawing.Bitmap pBitmap = new System.Drawing.Bitmap(iWidth,
iHeight);

System.Drawing.Graphics pGraphics =
System.Drawing.Graphics.FromImage(pBitmap);

IntPtr iHDCWindow = User32.GetDC(hWndWindowToCapture);
try
{

IntPtr iHDCGraphic = pGraphics.GetHdc();

//System.Drawing.Graphics tg = System.Drawing.Graphics.FromHdc( hDc );
iRetVal = StretchBlt(
iHDCGraphic,
0,
0,
iWidth,
iHeight,
(int)iHDCWindow,
pRect.iLeft,
pRect.iTop,
iWidth,
iHeight,
SRCCOPY | CAPTUREBLT);
}
finally
{
User32.ReleaseDC(hWndWindowToCapture,iHDCWindow);
}
return pBitmap;
}