I saw that your DataKeyNames setting in GridView control is like this
DataKeyNames="projectID"
Then I guess that your key name is projectID not prID, isn't it? If so, you could get data for the selected row as this line:
string id = GridView1.DataKeys[e.RowIndex]["projectID"].ToString();
And you should also add this column:
<asp:BoundField DataField="projectID" HeaderText="prID" SortExpression="projectID"/>
Did you try that?
In other way, you could try to use TemplateField instead
<Columns>
<asp:TemplateField HeaderText="prID" SortExpression="prID">
<ItemTemplate>
<asp:Label ID="lblPrId" runat="server" Text='<%# Bind("prID") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="projectName" HeaderText="projectName"
SortExpression="projectName" />
<asp:BoundField DataField="projectType" HeaderText="projectType"
SortExpression="projectType" />
</Columns>
And this code to get data from prID column in GridView1_RowUpdating event handler:
Label lblPrId = row.FindControl("lblPrId") as Label;
string prId = lblPrId .Text;
Sorry if this doesn't help.