I just modified a TTS1 app of mine to output a 700 character string, and it worked fine (except that it's using repetitive numbered phrases, and it's getting a bit tedious listening to it over and over and over again!)
So the differences are:
1/ I'm outputting to the speaker, not a WAV file, and
2/ is in English, not Italian (although I'm sure it'd sound better with an Italian accent).
Does yours output long strings to the speaker? I'm wondering if there is some size limit on the output WAV file size, given that string length does not seem to be the constraint.
Just in case you'd like a 700 character test string (or you're having trouble sleeping at night...)
Dim Temp As String = ""
Temp = Temp & " Now is the time for all good men to come to the aid of the 001 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 002 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 003 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 004 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 005 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 006 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 007 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 008 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 009 party."
Temp = Temp & " Now is the time for all good men to come to the aid of the 010 party."
Log(Temp.Length)
TTS1.Speak(Temp, True)