Warning: Wrong parameter count for strstr() in BackgroundProcess.php on line 55

Hi, on one of my servers I get this error message with each function I use with custombuild.

Executing /usr/local/directadmin/plugins/custombuild/admin/build set_fastest

Warning: Wrong parameter count for strstr() in /usr/local/directadmin/plugins/custombuild/admin/tools/BackgroundProcess.php on line 55
Background process has not been started!

I'm using these versions:
Directadmin: 1.50.1
Custom Build: 2.0.0 (rev: 1568)
Apache: 2.4.23
Nginx: 1.8.0