Delphi Parameterised Query won't work - sql

Question

I'm only a beginner in learning to use Parameterised Queries as I used to do a lot of concatentating before. I've been trying to get this query below to work. It is a simple 'Book' table, with a field called 'BookTitle'. I have a simple textbox where I invite the user to enter any title...and it should run the query below to find if that book exists. Below is my code that, when run, manages to compile. However, when an entry into the textbox is added and the button to run the query is pressed, a Debugger Exception Notification appears with the following statement.
Debugger Exception Notification: Project Project1.exe raised exception class EOleException with message 'Arguments are of the wrong type, are out of acceptable range, or are in conflict with one another'.
I then have the option to press 'Break' or 'Continue'. If I press 'Break', the line:
qbook.Parameters.ParamByName('BookTitle').DataType := ftString;
is filled with a purple/red colour (not sure what this means?).
That said, if I press 'Continue', the program will work as expected, and will continue to do so. Here is the code i've been testing.
procedure TForm4.btnRunQueryClick(Sender: TObject);
var BookEntry:string;
begin
BookEntry:=edtBookTitle.Text;
qbook.SQL.Text:='SELECT BookTitle FROM Book WHERE BookTitle = :BookTitle';
qbook.Parameters.ParamByName('BookTitle').DataType := ftString;
qbook.Parameters.ParamByName('BookTitle').Value := BookEntry;
qbook.Open;
end;
Further points to note: The components in my Delphi form are as follows
a TADOQuery named 'qbook',
a TDataSource,
a TDBGrid,
aTEdit into which the user enters their desired search criteria and
a TButton that once pressed, initiates the query.
With regards to the database, it is:
a MySQL database (Community Edition)
a table named 'Book', where BookID is the PK and is of INT data type.
a field entitled 'BookTitle' which i've set as VARCHAR(35). It is not part of the key. However, it is in the BookTitle field, that i want to apply my query.

Answer 1

NOTE: This answer was posted based on the original code in the question, which has been edited to match what is in my answer. See the question's revision history for the first version of the question on which my answer was based.
The solution you saw in the other post was correct; it was just for a standard TQuery and not TADOQuery. TADOQuery requires a couple of minor syntax changes:
Use Parameters.ParamByName() instead of Parameters
Set a DataType for each parameter before using it
Use .Value instead of .AsString
Here's a corrected version of your code (which also includes setting a value for BookTitle before using it.
procedure TForm4.btnRunQueryClick(Sender: TObject);
var
BookEntry:string;
begin
BookEntry := 'Some book title'; // or QueryEdit.Text or whatever
qbook.SQL.Text:='SELECT BookTitle FROM Book WHERE BookTitle = :BookTitle';
qbook.Parameters.ParamByName('BookTitle').DataType := ftString;
qbook.Parameters.ParamByName('BookTitle').Value := BookEntry;
qbook.Open;
end;

Answer 2

I have never known a string type query parameter need the datatype or whatever set, I would simply remove any reference to the datatype.
After all, if it hurts when you bang your head on a wall, just stop banging it.