[Solved] ASP.Net Error: IList does not contain any definition for ToList

Hi,

when building the solution .NET C# using VS 2019

I have this error

`CS1061 Error 'IList <IElement>' does not contain any definition for 'ToList'.Are you missing a using directive or an assembly reference?`

on this line

`List<IElement> lst = HtmlConverter.ConvertToElements(dt.Rows[i]["contents"].ToString()).ToList();`

but strangely the website works fine...

Pls can you help me?