tuplesort error from create index (?)

Howdy:

I am running Postgres 7.1 on Mandrake Linux 8.0,
kernel version 2.4.16.

I am trying to create an index on a table:

[snip]

database=> create index key_i on class (contract, memberid, date)

[/snip]

and I get the following error:

[error]

ERROR:  tuplesort: unexpected end of data

[/error]

Never seen this before; have created an index on this table without
seeing a problem.  That is NOT to say that this has never happened
before: I've just not seen it before.

Does number of records have anything to do it this?  I'd think not, but
I suppose it doesn't hurt to ask.  By the way, I have 4699631 records.

Thanks!

-X