SYMPTOM:
In Strategy 10.x running on Windows 2008 R2 machine, more than half of the subscriptions fail to run (more than 40 subscriptions, each subscription has over 10 dataset reports) when “Number of connections by Priority” set to an extremely high number (High 400, Medium 400, Low 400) as shown below:

Below entries can be observed in DSSErrors.log:
System Error 0x00000008 (8): --- Not enough storage is available to process this command.. Connection String: DSN= XXX;UID= XXX;. 2014-05-09 02:43:08.546-05:00 [HOST:XXX][PID:14308][THR:13296][Query Engine][Error][0x80042300] QueryEngine encountered error: Connection::Connect failed. Unable to connect. Error type: System call error. Could not spawn process. System Error 0x00000008 (8): --- Not enough storage is available to process this command.. Connection String: DSN= XXX;UID= XXX;.. 2014-05-09 02:43:00.918-05:00 [HOST:XXX][PID:14308][THR:9884][MultiProcess][Error] Could not spawn process. 2014-05-09 02:43:08.624-05:00 [HOST:XXX][PID:14308][THR:12268][Distribution Service][Error] FAILED SUBSCRIPTION 'document5': Error Msg: Error in MSIJob Execution. Error Code 0x80004294. Instance ID = 16B33B9F475DB7445BCD10936A7C2761, Contact (DS_USER1, F3E12D204EC04AD1292628A823A0C7DB), User (DS_USER1, F3E12D204EC04AD1292628A823A0C7DB). Stop in 'MSIDeliveryEngine::PreTransmissionNotification, Delivery Component of Distribution Service' <Scheduler Execution ID = B79597E1439E895FACF69893070C7656>