Unhandled exception in PGAdmin when opening 16-million-record table

A customer was reviewing the database that supports the application we
have provided. One of the tables is very simple, but has over 16
million records. Here is the table's definition:

CREATE TABLE feedback
(
charge integer,
elapsed_time integer, -- number of elapsed minutes since data began
recording
tag_type character varying(24), -- Description of tag being recorded
tag_value real, -- value of tag being recorded
status smallint, -- PLC Status, recorded with Control PV only
stack integer, -- Not used
heating smallint DEFAULT 0, -- 1 for heating, 0 for cooling
cooling smallint DEFAULT 0 -- not used
)

As you see, there is no primary key. There is a single index, as
follows:

CREATE INDEX feedback_charge_idx
ON feedback
USING btree
(charge);

In PGAdmin, the customer selected this table and clicked the grid on the
toolbar, asking for all of the records in the table. After twenty
minutes, a message box appeared saying that an unhandled exception had
happened. There was no explanation of what the exception was. The
database log does not contain any information about it. The PGAdmin
display did show a number of records, leading me to believe that the
error happened in PGAdmin rather than anywhere in PostGres.

Can anyone explain what is happening?

The customer is using PostgreSQL 8.4.5 (we just updated them within the
last few days) and PGAdmin 1.10.5 on a Windows Server 2003 box.

I see PGAdmin is now up to 1.12.1. I suppose the first thing I should
do is update their PGAdmin.

Thanks for your help!

RobR