This error occurs when opening a page, or an article, or when applying a format to an article element.

The causes may be:

1.The format that is assigned or being assigned contains link to a style library that has a duplicated style (two or more styles with the same tag name) in it.

2.The format that is assigned or being assigned contains link to more style libraries and two or more of them have duplicated style (a style with the same tag name) in them.

To correct this error

Edit the format in EdAdmin4, and locate the duplicated style, or libraries containing duplicated styles.

1.Remove the duplicated style or rename it.

2.Unlink one of the libraries from the format.