It appears that you are missing some curly braces within your crossjoin:

change this section:

non empty({

[first twelve], [Accounting Date].[Month].[Remaining Months]

--* [Procedures].[Billing Groups].[Billing Groups].ALLMEMBERS

}) on rows

to this:

non empty({ [first twelve], [Accounting Date].[Month].[Remaining Months]}

* {[Procedures].[Billing Groups].[Billing Groups].ALLMEMBERS}) on rows