How to use If condition in SSRS?

Hi,

I want to find out if N_DT and O_DT is same then disply it or leave it blank in SSRS for one field value.

For this I am using below expression,

=IIf(Fields!N_DT.Value = Fields!O_DT.Value, Fields!N_DT.Value, "")

but this is not working and it is showing me as #error.

Can someone please check and let me know what I am doing wrong or is there any other solution? Thanks.

Just for example, N_DT and O_DT  have below kind of values in DB.

N_DT =  NULL, 2011-01-01, ''(Blank)

O_DT =2011-01-01, NULL

Vicky