I have finally found what was wrong and how to stay connected to my drive.
I a set a Node guarding beat of 1 sec pulse (My network is only between a master and a slave so the fast timing is not critical)
I have a sync pulse of 100ms pulse beat. (sb 7)
Now I have a drive that stays in operationnal mode.
With my setting, i have found out that cycling the sync fonction is usefull only if the data gather from the drive (drive status) need to be constantly refreshed. It was my case here. If you don't need the drive status constantly, you can use the sync on demand.
At every sync, the drive send is pdo ( from the drive programation )
If you have a lot of node in your network, you have to calculate the frequency of the sync in function of this fact
A node can send only one TPDOS between each sync pulse and recieive only one RPDOs in the same life time. If a node send two tpdos in one sync period, the communication fail. So, you have to calculate how many time it taking to your node to send data's and makes sure there is enough space in your sync period. The exact calculation is an hard process and is needed only if you have a very active network and can be find in CANINMOTION site (where all the can standard are describe.
The only thing i can say about Canopen Protocol is this,
everything must be perfect to work and if you cannot understand what is happening in the network unless you have a sniffer and, you have to be armed with a lot of patience if you want to dig in this stuff. Still, once it is working, it is a fast and efficient way to communicate.