ltsWriteBlock: failed to write block XX of temporary file. Perharps out of disk space...

I have a database and a table with 70000 records (which i dont think it's
too much)
I join this table with another of about the same size and put a record
restriction (WHERE) and everything works out fine, but when I put two SUMs
over a couple of fields and add a GROUP BY  I keep getting this error,
ltsWriteBlock: failed to write block 27231 of temporary file               Perhaps out of disk space?

I checked and I have over 1GB free so I figure this must have something to
do with configuration parameters.

I'd appreciate any help.


Ligia