Hi Shreya,
this error message is produced by the Zend server, it's quite weird.
Do you have access to the php error logs of your hub server (this error seems to me to be on the hub server)? And also the php error logs of your Moodle site?
Can you post the errors that got diplayed when you reproduce the issue (Moodle dev debug mode should be enable on both site and hub)?
Thanks,
Jerome