Null integer not allowed in MySQL 5 ???

Hi All,

I have very weird problem. I'm trying to setup replication between two database servers - one MySQL 4.1, the other 5.0. It's only for testing purposes, as we're going to switch to the newer one once we're happy with tests.

However, after i import SQL dump, databases looks identical. However, MySQL 5 after running query:

INSERT INTO tblpolicylist (
ClientID, ProductGroup, Product, ProductType, RefID, PolicyStatus, Referer, OfferID , OwnerID
) VALUES (
'112402','Household','1','22','079580298' , 'New Business' , '' , '' , '91'
);

is coming back with error "Incorrect integer value: '' for column 'Referer' at row 1' " . It's interesting, cause on MySQL 4.1 the same query is working just fine. Table is exact repliaca of the one from 4.1, Referer field is integer, with null allowed... Of course if I replace '' with '0', query is working fine, but I need to have this value null... It's also causing problems with replications, as similar queries are returning error on 5.0 slave.

Any ideas?