This is part of the changes of the latest release as we mentioned in previous emails.

For more details, see the documentation pages:
http://code.google.com/apis/chart/interactive/docs/release_notes.html#whatsnew

and specifically for this issue:
http://code.google.com/apis/chart/interactive/docs/customizing_axes.html#Help

Converting the column into string is indeed the proper solution (and not a temporary
workaround).

Did you convert Date to String in your input data or did you cast it later?

After converting to string via changing addColumn to use a string and changing the addrow
calls to use String rather than date i do get my stacked column back.
But there are no labels on the x axis for the dates.

taking the second example and plugging it into the playground produces emptiness.
How do i get the xaxis labels back now that its been converted to a string?

I got the same error on a column chart (not stacked or grouped). I fixed it by adding
an empty first column as outlined under "I do not want domain axis values" here:
http://code.google.com/apis/chart/interactive/docs/customizing_axes.html#Help

I have no idea what "domain axis values" are, and it seems weird that adding an unlabeled
empty column is the recommended fix, but at least it worked :)

It's very frustrating that a perfectly good column chart that was working yesterday
is broken today...

bquirion:
We'll need an example to see what you mean.

rick.terrill:
"domain axis" is explained in that page you linked: http://code.google.com/apis/chart/interactive/docs/customizing_axes.html.
The changes introduced in this released (a) are considered required by the team in
order to provide consistent and coherent API across all charts, and (b) were communicated
several times during the past 3 months.

Look at the Data Format section of the column chart documentation for the required
data format.