You can build a second Xeno Anthropology Center when you upgrade it to the Universal Outreach Center.
The problem is that the preclusions list in ImprovementDefs.xml contain non-existent names (they contain spaces).
<Preclusions>
<Improvement>Xeno Anthropology Center</Improvement>
<Improvement>Universal Outreach Center</Improvement>
<Improvement>Future Studies Center</Improvement>
</Preclusions>
The fix is to either correct the specified preclusion names, or correct the internal names for them.
The most maintenance friendly solution would be to do both, eg: change the preclusion "Xeno Anthropology Center" to "XenoAnthropologyCenter" and also update the improvement internal name from "XenoAnthropology" to "XenoAnthropologyCenter" (and its linked string entries in the ImprovementText.xml).