Unable to add a resource to a project

Hi,

Difficult to analyse error that generates no log.
Possibly, can you open browser console, go to tab network and check access to php files (you can enter a filter).
Then you play use case, and check last call to php : there should be a response tab, please post its content here.

NB : it seems you are on V11.3.2, this is not the latest patch of V11.3, you should at least migrate to V11.3.3.
Also note that support on this forum is restricted to latest stable version, so we highly advise you to migrate to V12.1.2 (or V12.1.3 that is under deployment)