Select the duplicated rows ?

Hello pgsql users, I'm having trouble in select statement:

I had one table(test) such as follows:
rowid int primary key,
name char(20)
....

I try to compare the attribute name, and want to select
all duplicated rows that had same name.

I create SELECT statement as follows:
select rowid from test
where name in (select name from test group by name
having 1<count(name));

But, this statement is not executed.
Abnormally terminated with next messages:

test=> select rowid from t where name in (
test-> select name from t group by name having 1<count(name));
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally before or while processing the request.
We have lost the connection to the backend, so further processing is impossible. Terminating.

What's wrong?

Do you have any idea?
Plz, help me. Thans in advance!

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