Hello friends:
Happens to me the same error " Error sending command switch , check device / hardware ! " when I update the device status from the application. HOWEVER from the device button it works well.
I tested with serial GW (internal GPIO ) and GW LAN , with the same results.
The traces of the device and the GW are:

Device type: light node: 3 child: 6

Command Msg GW Msg Device
On button 3; 6; 1; 0; 2; 1; send 3-3-2-0 s=6,c=1,t=2,pt=2,l=2,sg=0,st=ok:1
read: 0-2-3 s=6,c=1,t=2,pt=2,l=2,sg=0:1
This is an ack from gateway
Incoming change for sensor:6 , New status: 1
On Domoticz 3; 6; 1; 1; 2; 1; read: 0-2-3 s=6,c=1,t=2,pt=0,l=2,sg=0:1
send 3-3-2-0 s=6,c=1,t=2,pt=0,l=2,sg=0,st=ok:1
This is an ack from gateway
Incoming change for sensor:6 , New status: 1
Off button 3; 6; 1; 0; 2; 0; send 3-3-2-0 s=6,c=1,t=2,pt=2,l=2,sg=0,st=ok:0
read: 0-2-3 s=6,c=1,t=2,pt=2,l=2,sg=0:0
This is an ack from gateway
Incoming change for sensor:6 , New status: 0
Off Domoticz 3; 6; 1; 1; 2; 0; read: 0-2-3 s=6,c=1,t=2,pt=0,l=2,sg=0:0
send 3-3-2-0 s=6,c=1,t=2,pt=0,l=2,sg=0,st=ok:0
This is an ack from gateway
Incoming change for sensor:6 , New status: 0

A Someone comes up with an idea?