MySQL reported an error: Can’t create a new thread (errno -1)

  mysql, question
Can't create a new thread (errno -1);  if you are not out of available memory, you can consult the manual for a possible OS-dependent bug

When I opened the website, I found mysql reported an error. The log is as above.
Can you tell me how to solve this problem?
Mysql Version: 5.6
Server: windows server 2003 32-bit
Memory: 16G
Number of websites: more than 1000

There is not enough memory.