Thx4 your support! I gave up on fixing the old install and started over with brand new install of OH2.4: All was up&running in 45mins!! MQTT2.4 with embedded broker works like a charm. On top the Mysensors MQTT GW Ting was online with 1-click! All my MYsensor nodes where recognized immediately! What a relief!
Hope someone will update Mysensors docu so others will be spared the pain...

@waspie tried that, still same errors...
What should be the entries in the org.eclipse.smarthome.mqtt.cfg file ?

I have configged the embedded broker in right way, broker is online on localhost.
I tried to connect Mys mqtt gateway to Embedded mqtt broker in paper UI:

Broker Name
MQTT Broker (-> not sure about this name....??)
name of the MQTT broker as defined in the org.eclipse.smarthome.mqtt.cfg file``` (-> if I check this cfg file there is NOTHING about the embedded broker, only old Musquitto stuf...)

All is on default port 1883 on both sides...

I get fault in OH log file:

2019-02-10 23:40:56.626 [ERROR] [al.protocol.ip.MySensorsIpConnection] - Failed connecting to bridge...next retry in 10 seconds (Retry No.:15)

Hi all, I am a Newbie an trying to get OH2.4 to work with MySensors nodes.
I have a MYS Mqtt ethernet GW up&running (seems to work, can talk to other sensors)
Now I can't get MQTT thing/broker/binding to work in OH2.4. I first tries the manual above, then I read that Musquitto is not needed any more....right??
I have to use MQTT 2.4 Ting binding and MQTT broker right? -> I have installed this and have MQTT broker running on localhost (online) (no channels addes in MQTT broker)
I have added in Things: MysensorsMQTT gateway: broker name: "MQTT Broker" and 'startup check' and 'sanity check' ON
Then I checked from the CLI the file "org.eclipse.smarthome.mqtt.cfg" ->there was still the musquitto entries I made... Also in mqtt-eventbus.cfg was still broker=musquitto. What do I do with this??
In OH log I get errors:

****2019-02-10 21:52:35.274 [me.event.ThingUpdatedEvent] - Thing 'mysensors:bridge-mqtt:9954d183' has been updated.

2019-02-10 21:52:35.682 [hingStatusInfoChangedEvent] - 'mysensors:bridge-mqtt:9954d183' changed from UNINITIALIZED (HANDLER_INITIALIZING_ERROR): org/openhab/binding/mysensors/internal/protocol/mqtt/MySensorsMqttConnection$MySensorsMqttPublishCallback to INITIALIZING

2019-02-10 21:52:35.685 [hingStatusInfoChangedEvent] - 'mysensors:bridge-mqtt:9954d183' changed from INITIALIZING to UNINITIALIZED (HANDLER_INITIALIZING_ERROR): org/openhab/binding/mysensors/internal/protocol/mqtt/MySensorsMqttConnection$MySensorsMqttPublishCallback****
---*

Next problem:
I installed the MySensors Ethernet gateway thing in OH, configged it with IP of Arduino running the Mys GW. -> This Thing will NOT come 'online'. I can Ping the GW board, all looks OK in GW log:

0 MCO:BGN:INIT GW,CP=RNNGA---,REL=255,VER=2.3.1
4 TSM:INIT
5 TSF:WUR:MS=0
11 TSM:INIT:TSP OK
13 TSM:INIT:GW MODE
15 TSM:READY:ID=0,PAR=0,DIS=0
17 MCO:REG:NOT NEEDED
580 GWT:TPC:IP=192.168.178.87
1583 MCO:BGN:STP
1585 MCO:BGN:INIT OK,TSP=1
1588 GWT:TPC:IP=192.168.178.87
2590 GWT:RMQ:MQTT RECONNECT
2798 GWT:RMQ:MQTT CONNECTED
2801 GWT:TPS:TOPIC=mygateway1-out/0/255/0/0/18,MSG SENT
2807 TSM:READY:NWD REQ
2844 TSF:MSG:SEND,0-0-255-255,s=255,c=3,t=20,pt=0,l=0,sg=0,ft=0,st=OK:
0 MCO:BGN:INIT GW,CP=RNNGA---,REL=255,VER=2.3.1
4 TSM:INIT
5 TSF:WUR:MS=0
11 TSM:INIT:TSP OK
13 TSM:INIT:GW MODE
15 TSM:READY:ID=0,PAR=0,DIS=0
17 MCO:REG:NOT NEEDED
580 GWT:TPC:IP=192.168.178.87
1583 MCO:BGN:STP
1585 MCO:BGN:INIT OK,TSP=1
1588 GWT:TPC:IP=192.168.178.87
2590 GWT:RMQ:MQTT RECONNECT
2798 GWT:RMQ:MQTT CONNECTED
2800 GWT:TPS:TOPIC=mygateway1-out/0/255/0/0/18,MSG SENT
2807 TSM:READY:NWD REQ
2844 TSF:MSG:SEND,0-0-255-255,s=255,c=3,t=20,pt=0,l=0,sg=0,ft=0,st=OK:
3810 TSF:MSG:READ,254-254-0,s=255,c=3,t=21,pt=1,l=1,sg=0:0
3815 GWT:TPS:TOPIC=mygateway1-out/254/255/3/0/21,MSG SENT
636790 TSF:MSG:READ,254-254-0,s=255,c=3,t=0,pt=1,l=1,sg=0:99
636795 GWT:TPS:TOPIC=mygateway1-out/254/255/3/0/0,MSG SENT
637304 TSF:MSG:READ,254-254-0,s=255,c=3,t=1,pt=0,l=0,sg=0:
637309 GWT:TPS:TOPIC=mygateway1-out/254/255/3/0/1,MSG SENT
637815 TSF:MSG:READ,254-254-0,s=1,c=1,t=16,pt=2,l=2,sg=0:0
637820 GWT:TPS:TOPIC=mygateway1-out/254/1/1/0/16,MSG SENT
637827 TSF:MSG:READ,254-254-0,s=1,c=1,t=15,pt=1,l=1,sg=0:1
637832 GWT:TPS:TOPIC=mygateway1-out/254/1/1/0/15,MSG SENT
637838 TSF:MSG:READ,254-254-0,s=7,c=1,t=0,pt=4,l=4,sg=0:44
637844 GWT:TPS:TOPIC=mygateway1-out/254/7/1/0/0,MSG SENT
637850 TSF:MSG:READ,254-254-0,s=255,c=3,t=0,pt=1,l=1,sg=0:99
637855 GWT:TPS:TOPIC=mygateway1-out/254/255/3/0/0,MSG SENT
900006 TSF:SAN:OK

How do I proceed? Ive tried to find more posts on getting MySensors to work under OH24 but I think it is sooo simple that nobody has any problems to post....right?!
Hope you guys can get this Newbie back on track.... thx a lot!