TYPO3 Core

Hi Wim, how can one reproduce this?
Can you please tell the required steps to get this error message?

All warnings and errors are mailed to me (Setting of $TYPO3_CONF_VARS['SYS']['systemLog']).
The If I didn't do that, I never noticed the error.
I did a little bit of research and it seems to me that the error has nothing to do with installed extensions.
In the Typo3 code I can't find nothing of this kind.
Something to do with PHP?

To answer your question: I do nothing special. Just requesting a page of the website.

Ah, I see...
I could not find any reference to a Date class in the TYPO3 Core. Could you please search in your installation for something like "new Date()" or "class_exists('Date')". Thanks in advance.

The statement "class_exists('Date') ", I found in the extension "cal" (file /res/pearloader.php).
The "new Date()", I found in several extensions: "cal", "coago", "dam", "dam_catedit", "direct_mail".

Of these extensions only "cal" and "coago" are used. It is not "coago" because that piece of coding is not used by me.
Rest the extension "cal". I tested it and the errorlogging is caused by the statement "class_exists('Date').

In the BE too is errorlogging of class "Date".

Errorlogging occurs also for the extension "tue_breadcrumb". The class "tx_tuebreadcrumb_pi1" can not be found.
Source of the error is in typo3/sysext/cms/tslib/class.tslib_content.php, line 7022 statement "class_exists".
The "breadcrumb" however produces the output normally.

Resolved, no change required.

As Wim figured out, this is not core related, but a problem in cal or tue_breadcrumb. Please report the issue there again if this is not solved in recent extension versions.