Make sure that these two items in your ini file are in sync:
InstanceMaxRequests=5000
EnvironmentVars=PHP_FCGI_MAX_REQUESTS:5000
If the PHP_FCGI_MAX_REQUESTS is not set then PHP will kill the FCGI process after 500 requests causing the error above. Also, double check that you enter it correctly. The sample docs that is referenced here shows the syntax for using the .js file which is different from what you manually enter.
-Stephen