"Invalid Parameter Used" Error

I am trying to read images from a SQL database by utilising the memorystream class. However, whenever I try to create a Bitmap object from the stream I get the above error. The database records are generally created from .bmp files and the byte object (b) is being created no problems. I have a feeling it has something to do with the bitmap header? I have tried various offsets (78 seems popular on posts) but to no avail. Here is my code:

b = CType(oPicture, Byte())
'Open a stream and read in the Image
Dim ms As New System.IO.MemoryStream(b)
ms.Read(b, iOffset, b.Length - iOffset)
'Create Bitmap from Stream
bm = New Bitmap(ms) *Error occurs here*

Can anyone offer any suggestions?

Thanks in advance