Class 'Piwik_ClickHeat_Controller' not found

[LotekHeavy]

when I view the heatmap and click on the icon "showGroupLayout" , I got this error message displayed on my wiki site:

An error occurred
Class 'Piwik_ClickHeat_Controller' not found

and also a js error:

Uncaught TypeError: Cannot read property 'style' of null
showRadioLayout @ VM2012:29
xmlhttp.onreadystatechange @ VM2012:234

Only switching the group with the dropdown gives no error.

My System:

• ClickHeat = 0.1.5
• PIWIK = 2.15.0
• PHP = 7.0
• Apache / FastCGI