ErizoController 1 in xxx.xxx.xxx.xxx does not respond. Deleting it

hi all
when there hava more than 7-8 video streams, the crashes happened,the log
as follow:

terminate called after throwing an instance of
’boost::exception_detail::clone_impl<boost::exception_detail::error_info_injectorboost::thread_resource_error

'
what(): boost::thread_resource_error
ErizoController 1 in 222.174.255.34 does not respond. Deleting it.
[CLOUD HANDLER]: Warning! No erizoController is available.