Issue
When you access the K2 Management site, the tree view on the left panel is showing this error:

Resolution
You can try clearing the Management site's cache using the URL below:
https://<your K2 site url>/Management/CacheControl.ashx?m=Clear
For example: https://k2.denallix.com/Management/cachecontrol.ashx?m=clear
This will return Completed if successful:
