Gib mal das WizardForm.NextButton.Enabled := MyEdit.Text <> ''; in die KeyPressmethode.
Ich bin nicht sicher, wann das OnChange ausgelöst wird.
Alternativ benutze
Code:
function NextButtonClick(CurPageID: Integer): Boolean;
Called when the user clicks the Next button. If you return True, the wizard will move to the next page; if you return False, it will remain on the current page (specified by CurPageID).
Note that this function is called on silent installs as well, even though there is no Next button that the user can click. Setup instead simulates "clicks" on the Next button. On a silent install, if your NextButtonClick function returns False prior to installation starting, Setup will exit automatically.
und prüfe dein Eingabefeld + verweigere bei Bedarf das Weitergehen.