Indexing doesn't work - Popen_function_not_exists - by: joris

When I try to index I get the error Popen_function_not_exists.

Is there a fix?

Version of JiFile: 2.3
Version of Joomla: Joomla! 3.4.1
Operating system: Linux web192 3.10.54-20140916-1425-05f4076 / Apache
Php version: 5.6.8
If you working locally or on a host: hosted

Regards, Joortje