cursor already in use error

PostGreSQL 8.0beta1
I have a function that uses a cursor and it is giving me the error: cursor
"crsr" already in use when the parameters I pass in come from another table.

The function works fine when I call it by itself, such as select
PartNeedsReschedule(100,1) or select * from PartNeedsReschedule(100,1)
but when I try select PartNeedsReschedule(PartID,1) from Parts then I get
the error.

It seems that when I qualify the query such as PartNeedsReschedule(PartID,1)
from Parts where partid=100
then it works because it is only returning one row.

Is this a known problem with cursor based functions that they can not be
called by set based queries?
Is there a workaround?

Thank You
Sim