First, I've read more than once that the v1.69 patch in the GOG version is not sufficient. You'll need the critical rebuild of v1.69 for the Diamond version at
files.bioware.com/neverwinternights/updates/windows/english/NWNEnglish1.69HotUUpdate.exe (if you haven't done so already).
Next, you'll need all the required haks and/or overrides installed for the server you want to join. Typically, they will have a website that describes in detail everything needed. Apparently you are missing one of the CEP 2.3 files in your installation. Not sure why so if you did all the above already you'll need to either reinstall or contact the server admin for suggestions (it may be a recognised problem or conflict with the custom resources you have).
TBH, I am just as brainless when it comes to identifying the source of custom content issues except for going step-by-step, checking and verifying everything that was supposed to install actually did and there are no empty files. It can happen.