numeric problems

I'm using pgAdmin II version 1.3.82 , psqlODBC 7.2.3 ,postgreSQl 7.2.1. There is a problem when I do an SQL querywith a
fieldof numeric, for eample NUMERIC (10.2). Followingstaement causes an error such as "Unable to indentify anoperator
'>'for type 'numeric' and 'double precision'..."
 
select itemNo, listprice from itmt_info
where listprice  > 50.99;
And this one works.
select itemNo, listprice from itmt_info
where listprice  > '50.99';

It seems all numeric operators are not available on NUMERIC FIELDS. Is there
anyone has done somethings on this problems? Or should I change NUMERIC type
to FLOAT type?  Please advise, thank you in advance.

Jack