problem with bitmap

hi,
i need some help in graphics display of bitmap.
i load a bitmap from file, resize it and display it. when form is closed the bitmap is save to a config-file as byte[].
when i load the bitmap from config-file i get the following exception :
"rotatedImage.Palette" caused excetion of type "System.Runtime.InteropServices.ExternalException",ErrorCode = -2147467259
the error occurs at line rotatedImage.RotateFlip(rotateFlipType); (rotateFlipType = RotateNoneFlipNone) in resizeImage(..)
with this line removed no error occurs and the bitmap is displayed

// **********************************************************************************
public static Image resizeImage(Image image, int newwidth, int newheight, RotateFlipType rotateFlipType)
// **********************************************************************************
{
PixelFormat pxlfrmt = image.PixelFormat;
// clone the Image instance, since we don't want to resize the original Image instance
Image rotatedImage = (Image)image.Clone();

rotatedImage.RotateFlip(rotateFlipType);

Size newSize = CalculateResizedDimensions(rotatedImage, newwidth, newheight);
Bitmap resizedImage = new Bitmap(newSize.Width, newSize.Height, pxlfrmt);
resizedImage.SetResolution(72, 72);
using (var graphics = Graphics.FromImage(resizedImage))
{
// set parameters to create a high-quality thumbnail
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphics.SmoothingMode = SmoothingMode.AntiAlias;
graphics.CompositingQuality = CompositingQuality.HighQuality;
graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
ImageAttributes attribute = new ImageAttributes();
attribute.SetWrapMode(WrapMode.TileFlipXY);

Rectangle rect = new Rectangle(new Point(0, 0), newSize);
graphics.DrawImage(rotatedImage,rect,0,0,rotatedImage.Width, rotatedImage.Height, GraphicsUnit.Pixel, attribute);
}
return resizedImage;
}

any suggestions ? be free to ask for more code

thanks in advance
franz