In order to get the histogram, you do not need to have kept all the individual run data (although you can do this by turning on the "save family waveforms" (or whatever the button is called) on the main monte carlo form).
The most likely problem is that you've got the expression for the scalar wrong - perhaps it's referring to a specific results directory, or using the wrong name for the results. The best approach is generally to use the direct plot form, and then hit the "add to outputs" button - this should generate the correct expression.
Often the issue is with the ?results argument in any data access expression. You need to make sure this is referring to the alias name for the results - if you do a single run and then do:
Code:results()
in the CIW, and compare this (one to one) with:
Code:results(?noAlias t)
You want to be using the name from results() not results(?noAlias t) as the argument to your ?results keyword argument in the expressions.
Perhaps you can post the expression you're using here - and I can take a look to see if I can spot anything wrong with it?
There were some issues with swept PSS and monte carlo, but these were fixed back in 4.4.5/4.4.6 if my memory is correct.
Best Regards,
Andrew.