OK, I notice that there are 2 VLANs required, one as VLAN20 and the other as 'default'. Typically a default VLAN is considered to be a VLAN that untagged frames are assigned to. Because of this, a routed interface with logical units (sub-interfaces) is not going to work.
You need to configure routed virtual interefaces:
set interfaces vlan unit 1 family inet address 192.168.100.1/24
set interfaces vlan unit 20 family inet address 192.168.110.1/24
Assign them to vlans:
set vlans VLAN20 vlan-id 20
set vlans VLAN20 l3-interface vlan.20
set vlans default vlan-id 1
set vlans default l3-interface vlan.1
Assign these VLANs to the interface but ensure frames for VLAN 1 are untagged:
set interfaces fe-0/0/2 unit 0 family ethernet-switching port-mode trunk
set interfaces fe-0/0/2 unit 0 family ethernet-switching vlan members VLAN20
set interfaces fe-0/0/2 unit 0 family ethernet-switching native-vlan-id default
Hope this helps.
BTW the reason for the error on commit is because you had not used this command:
set interfaces fe-0/0/2 vlan-tagging
But you will need to delete all that to use this method.