Accumulated and interannual ssas mdx

Hello! I'm (more than) new in the issue of SSAS and MDX and I have seen several examples for calculating accumulated sounding Chinese to me. In these examples illustrate that the function that could / should be used is PeriodsToDate or Ydt,  but I can not display anything (no errors, but the result is NULL). I created several tests calculated members for use in SSRS and excel. These are three of the many tests that have been made ??without success:

CREATE MEMBER CURRENTCUBE.[Measures].prueba_acum AS sum([Measures].[IMPORTE GASTO],YTD([Dim Tiempo].[Año])), FORMAT_STRING = "Standard", VISIBLE = 1 ; CREATE MEMBER CURRENTCUBE.[Measures].prueba_acum_2 AS sum([Measures].[IMPORTE GASTO], PeriodsToDate( [Dim Tiempo].[Año], [Dim Tiempo].[Mes].currentmember ...