Having an almost identical problem.

Using:
NWNEnglish1.69HotUUpdate.exe
CEP_23_Full_C.7z
Setup3.4rc1a.exe
prccep2_merge.rar

Installed NWN, SoU, and HotU.
Hotpatched up to 1.69.
Installed CEP 2.3
Installed PRC 3.4rc1a
So far, no problems. Can create a new wizard in the Neverwinter Original Campaign, with no noticable issues.

Then I use the PRCModuleUpdater.exe to install the PRC Pack to the Neverwinter Original Campaign.

Now the new Wizard characters I create (and the pregen ones that I play) can't summon a familiar. I click the button on my hotkey bar, the character goes through the motions of summoning the familiar (including the bright spellcasting effect around the location where the familiar would be summoned), then nothing. No familiar. The ability is used up for the day, and the character can rest and try again with the same result.

The in game log says:
Peegog Pensinger summons familiar.
Summoned a creature.

I tried using the PRCModuleUpdater.exe to install the prc_ocfix to the Neverwinter Original Campaign. I thought that might fix the issue, but it didn't.

I tried using the PRCModuleUpdater.exe to install the prcc2 to the Neverwinter Original Campaign. This didn't fix it either.

I understand  Sharlyn from Moonsea had a problem that sounds an awful lot like this. And xwarren fixed it. But how? If anyone knows what the fix is for this, I'd be eternally grateful.