Help! -- MS Enterprise Library DAAB - Object must implement IConvertible

I am having real problems with the above error (which after searching on google seems to have been inherited from the old DAAB) when calling db.UpdateDataSet.

I am attempting to update a SQL database from a dataset with 8 or tables in them... under a transaction.

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Update:

This fault caught me several times and it transpires that it actually WAS down to an illegal casttyping....
I use NullableTypes and was passing a NullableDateTime directly where what I should have been doing was something like Convert.ToDateTime(MyDateOfBirthAsNullableDateTime.toString()).

So there you go!