How did you actually define the RPC in PB. As an example, I use (with SNC, btw) the following for a stored procedure that returns values with 7 places of precision:
function long stock_get_price_hi_lo(decimal an_stock_id,ref decimal{7} price,ref decimal{7} dly_hi_price,ref decimal{7} dly_lo_price,ref datetime last_sale) RPCFUNC ALIAS FOR "dbo.stock_get_price_hi_lo"
I'll also point out that you are using the RTM version of sql server 2008r2 - a big bad no-no.