I Have just Changed my Lights to LED and Now They Won't Turn Off?

If your KNX system was installed before 2014 the dimmers will not be suitable for mains LEDs. This is due to the extremely fast development of LED technology and the forced adaption of non incandescent lights. 

There are potential way to work around this, such as load compensators but for guaranteed compatibility, new dimmers will need to be installed for the circuits with LEDs.