Gee, first up, it always better to break into lines, so you can read what you have for the gridview.
you have this:
<asp:GridView ID="_people" runat="server" AllowPaging="True" AllowSorting="True" AutoGenerateColumns="False" CellPadding="4" DataKeyNames="personID" DataSourceID="SQLDataPerson" ForeColor="#333333" PageSize="50" HorizontalAlign="Center" OnSelectedIndexChanged="__people_SelectedIndexChanged" OnRowDeleted="_people_RowDeleted" OnRowUpdated="_people_RowUpdated">
Looking at above, you even have 2 "__" for the selected index changed. (that's not all that great".
I suggest you name the gv without the underscore.
So, do this:
At least now, we don't have potential "mix up" of _ or __ (2 of them). They are rather hard to read, or see.
So, you will then have to cut+paste your existing code to the "new" events, and then delete the old ones.
There (hopefully) not too much code here, and thus a re-generate of the events without a "very easy" to miss under score is what I suggest you try here.
Just a quick look at above, I don't see anything much wrong, but I would try a re-gen of the events like I did as per that screen cap. (so, you hit ctrl-space when under the quotes (" ") to get that pop option to "create new event" as I did above.