Dispaly modal form and showmessage error

Can you show us your code please.
A showMessage call has nothing to do with forms, so you must be doing something else as well.

The answer might lie in the help file on Showmodal (See the "Note" below)

Use ShowModal to show a form as a modal form. A modal form is one where the application can't continue to run until the form is closed. Thus, ShowModal does not return until the form closes. When the form closes, it returns the value of the ModalResult property.
 
To close a modal form, set its ModalResult property to a nonzero value.
 Note:
 If the form contains buttons with a ModalResult property set to a value other than mrNone, the form automatically closes when the user clicks one of those buttons and returns the ModalResult value as the return value of ShowModal.

Can you explain more.

can you please show some code like mikelittlewood requested?

i think below solution will work for you.
But believe that this not good solution. You have to find the reason.



ShowMessage('fgdfgdfg'); //your error message.
AddNewClassForm.ModalResult:=mrNone;

The call from form 1 to display the AddNewClassForm is from a button click as follows:

Add_New_Subject_Form.ShowModal;

The Add New Subject Form basically has 4 fields and two buttons a submit and a cancel. I want to check if the user presses the submit button that all fields have values entered, if not show an error and return to the form, if the form is completed correctly the database record is appended to the dataset and the user is returned ot the original form here is the submit code I hope it helps

begin
  If (AddFaculty.Text = '') or (AddSubjectName.Text = '') then
    begin
      ShowMessage('All form fields are mandatory. Please complete form to add new subject');
    end
  else
    begin
      Maintennance_Form.SubjectID.Text := AddRecNum.Text;
      Maintennance_Form.DBLookupCombobox1.SetText(AddFaculty.text);
      Maintennance_Form.Subject_Name.text := AddSubjectName.text;
      Maintennance_Form.Subject_AcaLvl.text := SelectYearCB.Text;
      Datamodule1.SubjectSource.DataSet.Post;
      Close;
    end;  
end;

I took out the dataset.post and close lines and put another showmessage in there, which should show the message and then return to the form but when this show message is displayed it still closes the add new subject form, which made me think it had something to do with showmessage and showmodal

Thanks

Jake

i agree with  rfwoolf.
You are closing your form with 'CLOSE' function.
So the model result of your Submit button must mrNone.