Well you seem to be stopping the server on the first call - Value will be 1, you hit the else-block, play that other wave and then stop the timer. That does not go with what you mentioned in your post.
Check value for 275, play the first wave. Check for 299, play the second wave and then stop the timer. That's what you need to do there.
[Update]
----------
In response to your comment, here's an untested (for obvious reasons) code snippet that should do what you are trying to do:
private void timer5_Tick(object sender, EventArgs e)
{
barlizard.Increment(1);
if (barlizard.Value == 275)
{
try
{
var MySoundPlayer1 = new SoundPlayer("sounds\\RedBuffwarning.wav");
MySoundPlayer1.Play();
}
catch (Exception MyError1)
{
MessageBox.Show("Wrong Somewhere: " + MyError1.Message);
}
}
else if (barlizard.Value == 299)
{
try
{
barlizard.Value = 0;
timer5.Stop();
var MySoundPlayer = new SoundPlayer("sounds\\RedBuff(1).wav");
MySoundPlayer.Play();
}
catch (Exception MyError)
{
MessageBox.Show("An error has occurred: " + MyError.Message);
}
}
}