Help Needed For Datediff Function For SQL Query

Hi Experts,
I am working on SSRS 2005, and I am facing a problem in counting the
no of days.
My database has many fields but here I am using only two fields
They are Placement_Date and Discharge_Date
If child is not descharged then Discharge_Date field is empty.

I am writing below query to count the number of days but is is not
working it is showing the error
"The conversion of a char data type to a datetime data type resulted
in an out-of-range datetime value."

select case
when convert(datetime,Discharge_Date,103) = '' then
datediff(day,CONVERT(datetime,Placement_Date,103), GETDATE())
else
datediff(day,CONVERT(datetime,Placement_Date,
103),CONVERT(datetime,Discharge_Date,103))
end NoOfDays
from Placement_Details
So please tell me where I am wrong?


Any help will be appriciated.
Regards
Dinesh