Is it possible to default all number data to numeric type?

My company had a old program with written by Powerbuilder. It work
fine in MSSQL 6.5.
Now, my boss required to use another SQL server.  Someone told me
PostgreSQL is totally free and powerful.  I installed it in a Linux
machine (RedHat 7 + PostgreSQL 7.1.2), and transfer the old data from
MSSQL 6.5 server. It work fine.
However, when I run the old program.  When I try to update some record
with numeric type field, it show error as below.

Unable to identify an operator '=' for types 'numeric' and 'float8'...
You will have to retype this query using an explicit cast.

The point is the software house closed, I can't find any programmer.
>_<
So, I want to know is it possible to set the numeric type to default??
Or any easy way to fix it up?

P.S. My English is bad, pls. forgive me.