Error in log for DPT 5.010

Dear all

I always get this error

[ERROR] [b.binding.knx.internal.bus.KNXBinding] - Value '0.0' could not be sent to the KNX bus using datapoint 'command DP 4/4/0 Stufe, DPT main 0 id 5.010, low priority' - giving up after second try: 5.010 Unsigned count: wrong value format: 0.0

The related item is.

Number Stufe					"Lüfterstufe	[MAP(]"	<lueftung>			{knx="<5.010:4/4/0"}

the knx DPT is a 5.010 (ABB fan coil actor)

Anybody an idea why I get this error (apparently a wrong data format, although, ABB specifies it to be a DPT 5.010)?

Thank in advance

Best regards