Missing WYSIWIG text editor toolbar

After moving WebAsyst to another server or also under other circumstances the toolbar of the WYSIWYG text editor (in product description and info pages editing sections) may disappear as shown in the picture:

It can be caused by a corrupted cache file on the server. To eliminate the problem remove a .gz file whose name begins with .cache.tiny_mce from the /temp directory, e.g. /temp/.cache.tiny_mce_163519bb3c6a38b8081f79633db27c24.gz.

Removing that file will make WebAsyst create a new cache file and restore normal functioning of the WYSIWYG text editor.