Whats this error?
You cannot multiply "empty" things.
You probably have two textboxes or labels without anything set. Set these to 0 on initialise
This is my blocks...
There is no undefined multiplication in it.
There is even a notifier for an empty textbox.
The notable thing is that there is something in this tag that initially the tag text should be empty.
unless it is happening somewhere else you are not showing in your blocks
Is your Clock set to TimerEnabled in the Designer ?
It should look like this:
A clock timer to trigger an input calculation?
No!
You could suffer from premature evaluation.
No
The calculations are done after the annunciator and the clock are finished
This is for the sake of aesthetics
Of course, in my opinion..
Since the calculation speed is fast, this is not noticeable.
Wow!! 
Yes, that's right
The error has been corrected...