group_concat of flex table values issue

Hi,

I have a flex table and I am trying to concatenate values using :-

set search_path to public;

select a.id , group_concat(a.values) OVER (PARTITION BY a.id)
from (
select __identity__ as id, mapitems(sourceGroups) OVER(PARTITION BY __identity__) from testJSON
) a;

I get the error :-

 16:46:15  [SELECT - 0 row(s), 0.000 secs]  [Error Code: 2858, SQL State: VP001]  [Vertica][VJDBC](2858) ERROR: Could not find function definition

The group_concat function is there in our public schema.

I can select the value a.id and a.values I just can't seem to do a group_concat.

I have googled for a soluiton but come up blank.

Any ideas?

Thanks,