MySQL Unable to create thread error

[wc3garage82]

MyBB has experienced an internal SQL error and cannot continue.

SQL Error:
1135 - Can't create a new thread (errno 12); if you are not out of available memory, you can consult the manual for a possible OS-dependent bug
Query:
[READ] Unable to connect to MySQL server

that is the error generated by my forum's mybb
stoli server