Parse Error neaer NullOrder

I'm getting an error when my plpgsql function in 7.2.3 is called from Java.
The error is
Parse Error Near NullOrder.

When does this error occur. The function worked fine when I removed the
Order By Clause from it. But then When i checked....The field that I was
using in the order by clause, did not contain any null values. Then Why did
I get this error and why did it work when i removed the clause? I need to
insert it again.

PLease someone Suggest something. POstgres is functining cray in many
situations. Neither does not have a proper documentayion of error codes nor
does it throw errors when it should be thowing errors.

Thanx
Madhavi