Error while converting into Bitmap

I have a task of Embeding Image with text.it works fine in Ordinary Asp.Net Page but Ajax.
I have come accross the error"Parameter is not vaid" while converting Physical path of image into bitmap image.I am sending code(Aspx code and class file) with this mail kindly Let me know how to solve this error.
Code:
 
Aspx Page:

private void WaterImaging()
    {
        if (!string.IsNullOrEmpty(fuPictureImage.PostedFile.FileName))
        {

            if (!string.IsNullOrEmpty(txtEmbedText.Text) & !string.IsNullOrEmpty(txtLeft.Text) & !string.IsNullOrEmpty(txtTop.Text))
            {
               
 &nbs ...