Some text fields in WebUntis allow to enter formatted text. This is especially the case for "messages of the day" and "internal messages".
To guarantee security and a consistent behaviour of WebUntis not all characters / HTML tags are allowed. If you enter text that is not allowed a warning message appears.
The entered text contains symbols or formatting that can not be saved. Please try removing special characters or formatting.
If this messages appears even if you didn't enter special HTML tags it could be that the text was copied from a different application which added them.
In this case please try copying the text to a text editor that does not allow formatting and then copy it back to WebUntis or try using the new design of internal messages in WebUntis.