Request Failed (code 500, Internal Error) Close - ActiveS

I used ActiveScaffold to create my Rails application.

After I fill the fields and try to "Create" the new data, I get the
following:

Request Failed (code 500, Internal Error) Close

I don't know if this is caused by the "Date" field, which its value
looks like this:

Wed, 15 Sep 2010 00:00:00 %z

And, really don't know what "%z" is, why it appears, and how to remove
it.

Any ideas on that?

Thanks.