I think I found it.
I got a clue from this post:
http://groups.google.be/group/micros...d50703f0a298f7

I copied a cell in row 2, and pasted data validation in that column
for rows 2 - 13k-something. That makes it one continuous range with
validation. I repeated for 3 other columns with validation, who happen
to be next to each other.
After that I was able to save without any error.

I would like to say thank you to Debra Dalgleish.

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Amedee