Multi Value Parameters help

Hi Gurus

In the main dataset query i created a parameter "where  k.jlocat=:LOC or :LOC is null". These are ORACLE Parameters and hence the :. In another dataset i created a simple query as

select distinct jlocat as LOC

FROM TABLE1

Every thing works fine so far. Now i want to select multiple values for this i edited the @LOC parameter to select multiple values and changed my WHERE CLAUSE in the main dataset as where  k.jlocat=:LOC or :LOC='All'.

Now when i save and run the report , i cannot click on 'Select All' as it gives me an error:ORA-00907: missing right parenthesis.

I'm confused as where i'm missing the right parenthesis.Please need advice.

Thanks