Graph Closeness - Different result with gephi and NodeXL
The closeness of a node in a graph is defined as the reciprocal of the sum of all distances to other nodes.

Since your example is completely symmetric, we only calculate the closeness centrality of $A$.


distance $A\to B$ is 1
distance $A\to C$ is 1
distance $A\to D$ is 2


Therefore the sum of the distances is 4, and the closeness of $A$ is $1/4$. This shows that the NodeXL results are correct. I would advise you to have a look at the manual of Gephi to check how the closeness is computed here. It should be definitely be smaller than 1.