postmaster hangs on delete from

Hi,

I have a serious issue with delete from.

When I do something like:

"delete from CALC_INVOICE_DATA where PERIOD_END>='2011-01-01'"

the postmaster takes 100% CPU and then nothing happens.

Doing any type of select on the same table works just fine, I have tried
various forms of vacuums and re-import of data but the result remains the
same.

Does anyone have a clue on what might be wrong here?

/Magnus