A couple of things you need to remember about shared variables and sub-reports.  The name for the shared variable needs to be defined in every formula that it is used in the main report and subreport.  To get values back to the main report, the sub-report must be in a previous section to where you are looking at the shared variable in the main report (I hope that made sense).  The subreport cannot be suppressed or in a suppressed section (there are ways around this if you do not want to see the subreport).

I hope this helps.

Syntax is easy;
Shared numbervar (or currencyvar or stringvar, etc.) variable_name;

Now to get a value from the subreport, make sure that it is in a section prior to where you need the values in the main report.

Also make sure that the shared variable is defined in each function that you need it in the subreport and main report (if you want just display the value in the main report, then you just need the shared variable defined in the main report).   I think there are some tutorials on the web that show all this.

I hope this helps.