Another thing you may want to try is overriding the DNS on one of the computers to see if it makes a difference. Try just using a static of 8.8.8.8 and 8.8.4.4 or something to test. Could be some strange upstream DNS issue.
Adam R MS | CISSP, CISM, VCP, MCITP, CCNP, ITILv3, CMNO
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