Filemaker.php Class 'FileMaker_Command_Find' not found in

We run a webserver in a datacenter based on CentOS Linux. We have our website running on that server. For the client portal we use a connection to our local Filemaker 12 Server via FM_API_for_PHP_Standalone.zip. We have a good connection (tested with fmi-test sample database) to out local server. So that works.

We have run the filemaker php code for many years on the local server with no problems. Now I've moved the php code to the webserver and installed and configured FM_API_for_PHP_Standalone.zip correct (php date and php curl modules installed, path updated, etc). As said, the fmi-test sample runs correct on our webserver to the fms12 server.

My code generates errors, after logging in, and I cannot find what causes these errors. 

Fatal error: Class 'FileMaker_Command_Find' not found in /home/admin/FileMaker/FileMaker/Implementation/FileMakerImpl.php on line 122

My gut feeling tells me this is something simple, but what?

Can someone help me out here? Thanks in advance.