The "NoData/Error" image for caches can be handled via the resource file "synergis_weboffice_user.xml" (C:\Tomcat\webapps\<WebOffice-Applikation>\client_workspace\JSXAPPS\weboffice\jss\synergis_weboffice_user.xml).

"'NoData/Error" image for caches in WebOffice html client
Add the following line with a link to the "NoData/Error" image to the resource file:
<record jsxid="cache.tile.error" type="jsxsrc" eval="1" jsxtext="jsx3.resolveURI('jsxapp://weboffice/images/notile.png')"/>

Configuration of a "NoData/Error" image in the "synergis_weboffice_user.xml" file