While comparing the files I have in my mod folders with the base files in the 4.0 beta, I discovered that I had a copy of StarbaseModuleDefs.xml that attempted to fix a bug in 3.96, that apparently has not been fixed in 4.0.
The CulturalForumModule has:
<Prerequ>
<Techs>
<Option>CulturalExchange</Option>
</Techs>
<StarbaseModule>CultureRingModule</StarbaseModule>
</Prerequ>
Which I think should be:
<Prerequ>
<Techs>
<Option>CulturalInfluence</Option>
</Techs>
<StarbaseModule>CultureRingModule</StarbaseModule>
</Prerequ>
i.e. CulturalInfluence instead of CulturalExchange.
If I'm right, please add this to 4.0. If I'm wrong, please let me know so that I delete that from my mod folder.