Forms Data Controls :: Error When Inserting Into Table - Cannot Insert Explicit Value For Identity Column In Table

I am working on a web app for an online photo album. It is the last project in Scott Mitchell's book: "ASP.Net 2.0 in 24 hours".

I am creating a page where users can enter new photo images. The functionality for uploading an image will come later. I am working on just inserting a new row into the Pictures table with an optional category, a required title and a required description.

I am getting an error when I try to insert a new row.

Here is a screenshot of the page with a shot of the dropdown list.

The Categories are user-specific. I am getting the correct values retrieved.

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There are two pretty simple database tables involved here.

NOTE: The CategoryID and PIctureID are both autoincrement integer columns.

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The page uses a DetailsView that uses a SqlDataSource that uses the Pictures table. (The DetailsView's Default Mode property is set to "Insert". The "Enable Inserting" checkbox is also checked.)

The dropdown list uses a dropdown control that uses a SqlDataSource that uses the Categories table.

When the "Insert" button is clicked the CategoryID value associated with selected (Category) Name on the dropdown list will be used along with the Title and Description values to insert a row in to the Pictures table. (If no Category value is selected, then a null value will be used for the CategoryID. This is OK because the CategoryID column in the Pictures table allows nulls.)

My problem is that I am getting this error:

Cannot insert explicit value for identity column in table 'Pictures' when IDENTITY_INSERT is set to OFF.

(FYI: I have the full version of both Visual Studio and SQL Server.)

Here is my source code for the page:

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