Data validation drop down list doesn't work after saving closing and reopening workbook.

Data validation drop down list problem.

I have a few drop down lists that seem to be working fine at least initially. They are arrays so when in the data validation area, I press control shift and enter. I save the workbook, and open it later to work on it. Now all of the data validation drop down lists don't work properly. I go into the data validation area, re-commit with control shift and enter and now they work fine again, I haven't changed anything with the formula. I've looked everywhere and can only find one line replies for formula's that work for another person's workbook with no explanation whatsoever as to why to do it a different way.

Any suggestions as to what I'm doing wrong and more importantly WHY?

Many Thanks,

Can anyone help me out or at least explain why it would do this?