Pagliano got immunity to testify in front of the FBI; he's pleading the 5th when it comes to testifying in the Judicial Watch civil suit.
Because he wants to continue breathing.
Although the actual wording of the Fifth Amendment to the U.S. Constitution says a person shall not be “… compelled in any *criminal* case to be a witness against himself”, the right has been found applicable to civil actions as well. Natural persons in danger of facing criminal charges do not have to testify, answer interrogatories or produce documents about matters potentially incriminating to them.
A deposition is testimony. So is he in danger of facing criminal charges? Not unless he violates the terms of his immunity agreement with the Justus Department.
So it looks like Hillary is trying to have it both ways: hang it on Pagliano, “Why, I didn’t even know to have a password!” But wait—he’s got immunity.