COnditional Block in cross tab

[mrcool]

Hi Frnds,

                  Iam trying to use Conditional block in cross tab n its throwing the error Unable 2 build the cube.

Steps I folloed:
1)I have a value prompt with static choices like month,YTD,CM VS LCM,YTD VS LYYTDetc in prompt page
2) In variable I wrote condition like If Paramdisplayvalue('-----')='Month' then 1 n so on
3)I draged condtional block into the measures and trying to show the columns accoring to Prompts selected.
4)I have 2 measures in the Crosstab.With 1 measure its working fine.But Wen Drag the second measure,Iam facing this error.

Thanks in advance