Saving Image To Database From Picturebox - 2008 / Framework 3.5?

I have a form containing a listbox showing a list of image names. It's bound to the database table. When an image name is clicked it shows the image and imagename in a picturebox and textbox respectively. When no image is selected in the listbox, a new record can be inserted by browsing a new image in the picturebox by an openfiledialog, writing the imagename in the textbox and pressing the OK button. When an image is already selected, the record can be updated by pressing the same OK button. The data is saved into MSSQL Server 2005. Corresponding table fields are Keycode int autono, logoname nvarchar(50), logo image.Now the problem, when I insert a new data with an image everything goes fine but whenever I try to update an existing data with an image it throws an exception- 'A generic error occurred in GDI+.' at the following line- 'pic.Image.Save(ms, pic.Image.RawFormat)'. Surprisingly when I update an existing data without any image in the picturebox no exception is generated. I have crossed checked it and seems that the problem is just at one point- 'Updating the image from the picturebox'. My code to insert/update the data by OK button and to populate it by listbox doubleclick follows:

Code:
Private ms As MemoryStream
Private arrImage() As Byte
Private conn As SqlConnection

[code]....