You can reproduce this pretty easily, just create a new revision using arc diff and you should find a corresponding error logged on a taskmaster:
[2016-01-25 00:02:22] EXCEPTION: (PhutilProxyException) Permanent failure while executing Task ID 320. {>} (PhabricatorWorkerPermanentFailureException) Unable to load transactions: PHID-XACT-DREV-nhexnck64mngrhz. at [<phabricator>/src/applications/transactions/worker/PhabricatorApplicationTransactionPublishWorker.php:112] arcanist(head=master, ref.master=b87138356a9c), phabricator(head=master, ref.master=a9e2e6c5aab9), phutil(head=master, ref.master=f43291e99d36) #0 <#2> PhabricatorApplicationTransactionPublishWorker::loadTransactions(DifferentialDiff) called at [<phabricator>/src/applications/transactions/worker/PhabricatorApplicationTransactionPublishWorker.php:19] #1 <#2> PhabricatorApplicationTransactionPublishWorker::doWork() called at [<phabricator>/src/infrastructure/daemon/workers/PhabricatorWorker.php:122] #2 <#2> PhabricatorWorker::executeTask() called at [<phabricator>/src/infrastructure/daemon/workers/storage/PhabricatorWorkerActiveTask.php:171] #3 <#2> PhabricatorWorkerActiveTask::executeTask() called at [<phabricator>/src/infrastructure/daemon/workers/PhabricatorTaskmasterDaemon.php:22] #4 PhabricatorTaskmasterDaemon::run() called at [<phutil>/src/daemon/PhutilDaemon.php:183] #5 PhutilDaemon::execute() called at [<phutil>/scripts/daemon/exec/exec_daemon.php:125]
Underlying issue here is that the transaction is saved as a DifferentialTransaction rather than a DifferentialDiffTransaction.
mysql> select * from differential_transaction where phid = 'PHID-XACT-DREV-nhexnck64mngrhz'\G *************************** 1. row *************************** id: 15 phid: PHID-XACT-DREV-nhexnck64mngrhz authorPHID: PHID-USER-rihx4366f3aczsvc2wtb objectPHID: PHID-DIFF-fgt7avmnvsxgcbgzx5ci viewPolicy: public editPolicy: PHID-USER-rihx4366f3aczsvc2wtb commentPHID: NULL commentVersion: 0 transactionType: differential:diff:create oldValue: null newValue: true contentSource: {"source":"conduit","params":[]} metadata: [] dateCreated: 1453698141 dateModified: 1453698141 1 row in set (0.00 sec)