Custom card error: element doesn't exist

Hi all,

I’ve manually installed vacuum-card on my HA system and added to resources (yaml-mode).
Now I get the following error in the ui: Custom element doesn’t exist: vacuum-card

In the log file I get this error:

Logger: frontend.js.latest.202011112
Source: components/system_log/ init .py:193
First occurred: 00:12:42 (4 occurrences)
Last logged: 00:26:01

http://192.168.2.253:8123/local/vacuum-card.js:1:33 TypeError: Fehler beim Auflösen des Modulspezifierers “lit-element”. Relative Modulspezifierer müssen mit “./”, “…/” oder “/” beginnen.

Has someone an idea what went wrong?