From is not a valid date.

I am running Drupal 5.1 and recently upgraded from Date 5.x-1.2 to Date 5.x-1.x-dev.
I already had a number of event nodes that were successfully using Date fields.
However, since that upgrade, whenever I try to edit an existing event node or create a new one, I am unable to save the node, even if I change nothing. Every time i get the error such as:

date 8 From is not a valid date.

The number of the date varies, and usually i get several of them, but it never appears that anything is wrong or out of the ordinary with the data in my date drop down fields. and i even get errors on dates that are not filled out at all.

This has paralyzed my site. This is a live production site.
I have tried dropping back to Date Date 5.x-1.2. I have tried Date Head, re-installing Date 5.x-1.x-dev, nothing works so far to get rid of this problem.

Does anyone have a solution? Why can I not at least revert back to a previous version of Date? Has my database data somehow become corrupt? If so, what do I do?