"fetch type out of range" error message throwing

While executing the following code szNotes := SQL.FieldByName('Notes').AsString; throwing an "fetch type out of range" error message. I'开发者_开发技巧m using SQL Server DB, the field type is VARCHAR(MAX). How to resolve this issue, please guide me.

try to use szNotes := SQL.FieldByName('Notes').AsWideString;