MIssing Privilege When Trying To Execute Function on Another Schema

 Hi folks

I am tying to find out what privilege i need to execute a select statement using a function that was created by another schema owner and cannot figure what i need. Any assistance would be appreciated. I thought I had covered everything, but apparently not.

logged in as llprod_ro user exceuting on schema llprod

decode_subtype is function name

select subtype, llprod.decode_subtype(subtype) from llprod.dtree where rownum < 3;
                       *
ERROR at line 1:
ORA-01031: insufficient privileges

Thanks

Jim