Firstly, I would ensure that the cache data source test connection works fine at the server level. Then, in order to troubleshoot this error, I would enable the below logger category with debug level and refer the **vdp.log** file located under <DENODO_HOME>/logs/vdp to get more details about the error prompted in Virtual DataPort.
Execute the below predefined stored procedure in the VQL shell of Virtual DataPort Administration Tool, to enable the logger category as mentioned above:
For more details, refer to the similar community question [Exalsol as Cache DB](https://community.denodo.com/answers/question/details?questionId=9060g0000004EuUAAU&title=Exalsol+as+Cache+DB)
Hope this helps!