This situation occurs when the cache is not configured properly. So, in this scenario, I would follow the below steps:
* Make sure the cache is enabled at server level.
* Make sure that the connectivity is fine with the database specified for cache.
* To get more details about the error, check the vdp.log file present at `<Denodo_Home>/logs/vdp/`
Refer to a similar [Q&A](https://community.denodo.com/answers/question/details?questionId=9060g000000kAVpAAM&title=Full+Caching+in+Denodo+Express) for further information.
Hope this helps!