You are actually already reading the stream to a byte array, why not just stop there?
public static byte[] ExtractResource(String filename)
{
System.Reflection.Assembly a = System.Reflection.Assembly.GetExecutingAssembly();
using (Stream resFilestream = a.GetManifestResourceStream(filename))
{
if (resFilestream == null) return null;
byte[] ba = new byte[resFilestream.Length];
resFilestream.Read(ba, 0, ba.Length);
return ba;
}
}
edit: See comments for a preferable reading pattern.