Referential Integrity Problem on UPDATE

When I try to update my tblCompanies with

UPDATE tblcompanies SET tblcompanies.strname = 'Biscuit Inc' WHERE
tblcompanies.id = 18732;

I get the following error:
ERROR: tblcompanies_address_fk referential integrity violation -
key in tbladdress still referenced from tblcompanies

My settings:
- tblcompanies.addressid is a foreign key to tbladdress.id
- the constraint in tblcompanies for the address id is:
CONSTRAINT "tblcompanies_address_fk"
FOREIGN KEY ("addressid")
REFERENCES "tbladdress" ("id")
ON DELETE NO ACTION ON UPDATE CASCADE NOT
DEFERRABLE INITIALLY IMMEDIATE,
- I am using postgresql 7.2.1

Has anyone else had a similar problem, or do you know of a solution to
this problem?

Many thanks
;->