That's strange. I haven't seen this issue and I can't reproduce it with my own copy of 10.1.0.

Most likely there's something wrong with the configuration of your paclets. The easiest way to resolve this is to remove all the paclet configuration on your installation and reset Mathematica to it's installation default settings.

To do this, follow this article's instructions:

http://support.wolfram.com/kb/12464

If this doens't work, I would contact Wolfram Technical Support about the issue.

The functions fail silently without any error message. I just get back the input.

In[257]:= PersonData[Entity["Person", "BillGates::55r7v"], "BirthDate"]

Out[257]= PersonData[ Entity["Person", "BillGates::55r7v"], "BirthDate"]

In[251]:= MovieData[ Entity["Movie", "Avatar::y6ws3"], "ProductionBudgetAdjusted"]

Out[251]= MovieData[ Entity["Movie", "Avatar::y6ws3"], "ProductionBudgetAdjusted"]

In[254]:= MovieData["SampleEntities"]

Out[254]= MovieData["SampleEntities"]

In[258]:= CommonName[Entity["Country", "UnitedStates"]]

Out[258]= CommonName[Entity["Country", "UnitedStates"]]