Error: Server error, try reducing the number of threads. WPSCAN

[ivolangen]

Hi, i have a problem while brute forcing a website.
I am brute forcing a wordpress website and using Linux
If a start brute forcing the website i got a lot of errors
"Error: Server error, try reducing the number of threads. "
I tried a lot of things and reduced the threads to 1 but it does not solve the problem.
This is the code:

• sudo wpscan --password-attack xmlrpc --max-threads 1 -U ************** -P /opt/useful/SecLists/Passwords/Leaked-
  Databases/rockyou.txt --url ***************

Can somebody please help because it is a school project where the deadline is short from.