Server Error in '/' Application.

Compilation Error

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS1061: 'ASP.salary-increment.html' does not contain a definition for 'ddlinst_SelectedIndexChanged' and no extension method 'ddlinst_SelectedIndexChanged' accepting a first argument of type 'ASP.salary-increment.html' could be found (are you missing a using directive or an assembly reference?)

Source Error:

Line 56:                                     <div class="form-group">
Line 57:                                         <label class="col-form-label f-w-700" for="alighaddon2">Installment</label>
Line 58:                                         <asp:DropDownList ID="ddlinst" runat="server" OnSelectedIndexChanged="ddlinst_SelectedIndexChanged" AutoPostBack="True"></asp:DropDownList>
Line 59:                                     </div>
Line 60:                                 </div>

   Line: 58

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.7.2633.0