SQL: Converting Column Datatype from DateTime to Uniqueidentifier

Another day for weird annoying things.

I had a table on which I'd inadvertantly set a columns datatype to datetime when it should have been uniqueidentifier. The table was empty.

Resetting the datatype via script won't work due as SQL knows it can't implicitly convert the (nonexistant) data. So I tried using the GUI to change the datatype and I got incompatible operand errors. Tried doing an ALTER TABLE command and got the same error. Finally I tricked the little bugger by converting it to varchar first then to uniqueidentifier. Boom! Done. Sorted.