[DotGNU]cast to bitmap from resource file

[blt]

The following code compiles fine on VS.NET but under pnetlib 0.6.2 it does
not like the cast to Bitmap. Any idea what might cause this?

ResourceManager resourceManager = new ResourceManager("Bitmaps",
GetType().Assembly);
imgList.ImageSize  = new Size(32,15);
imgList.Images.Add((Bitmap)resourceManager.GetObject ("UnSelectedDir.bmp"));
imgList.Images.Add((Bitmap)resourceManager.GetObject ("UnSelectedFile.bmp"));
imgList.Images.Add((Bitmap)resourceManager.GetObject
("PartlySelectedDir.bmp"));
imgList.Images.Add((Bitmap)resourceManager.GetObject
("PartlySelectedIncrementalDir.bmp"));
imgList.Images.Add((Bitmap)resourceManager.GetObject
("FullySelectedDir.bmp"));
imgList.Images.Add((Bitmap)resourceManager.GetObject
("FullySelectedIncrementalDir.bmp"));
imgList.Images.Add((Bitmap)resourceManager.GetObject ("SelectedFile.bmp"));
imgList.Images.Add((Bitmap)resourceManager.GetObject
("IncrementalFile.bmp"));