Yes, I created an account because when entering the txid, it always failed(try later), but no I'm not a miner.
After signing in, I tried again, and it worked. The transaction has succeeded, problem solved (except for my multibit wallet password problem, but nevermind, i'll use an electrum wallet now).

Ok, so I tried viaBtc a few times, with no success ... until I signed in.
It said it succeeded, so I suppose I just have to wait.

And I searched the import private key in electrum but there is only sweep and export?!!?

Yes, that's it.
The first unconfirmed txId : c38b54275a9a0c157db8dd7e60249b1d91b428f3ed8e539015ee0f7e31b26eba
And the sweep unconfirmed one is unknown everywhere (blockchain info, blockr, blockcypher)

So, I found a the problematic private key and sweep it in electrum.
In the history tab, it says unconfirmed with the correct amount/Balance, but the transaction is not found in blockchain.info.
So what's next?

Yes, you're right,

what I don't understand is : is it just a multibit interface problem, or a transaction one? Do I just have to wait until the transaction finishes(which appears as "unconfirmed transaction" in blockain info)?
will the pb disappear once the transaction is over?

Anyway, I can't use the breadwallet method, for the other one, my procedure is this :
1/ install electrum and "create new wallet / already have a seed / option-bip39 seed / use my multibit seed&password.
2/ Get private keys from offline page "Mnemonic Code Converter".
3/ What then in electrum or armory? "sweep private keys" and then click on broadcast?

Hi hitec,
and thanks for your reply.
But it seems I just had a "lucky strike" and retrieved my wallet. I'll explain the procedure just in case, might work for other people as well  :
1/ uninstall MultiBitHD 0.5.1.
2/ Goto C:\Users\"username"\AppData\Roaming and delete MultiBitHd directory ( or just cut&paste it somewhere else just in case if you don't want to lose it )
3/ install MultiBitHD 0.4.1 (a previous version ).
4/ When asked, retrieve wallet with seed words.
5/ Be quick, as soon as it starts synchronizing you'll be able to click on finish before it becomes disable.
6/ It will ask you the password, type it here, it will work. (Everytime I waited the end of the synchro to type the password, it failed)

Of course, it worked for me, not sure it will work for anyone else, or if it's this specific procedure which corrected the situtation, but I think it's worth a try.

Hi guys, same problem for me, "transaction did not deserialize completely"
Isn't there any way to retrieve a wallet with another soft, if you have the seed phrase, the password and the timestamp?
Whatever the solution is, if someone could make a step by step procedure, it would be great. ( i tried a lot of things with electrum, which is stuck "synchronizing...".)

thanks everyone.