Campaign inexplicable locked
 

After beating the two first campaigns I could choose between mare nostra and the other one, in mediterrana sea,too. But after choosing Mare Nostra and winning the campaign, The previous that I could've choosen is now locked, it has a big X on it but it doesn't say that is locked. I can select it, it is highlighted as if it's playable but the START text is..."grey", I can't select it to start the campaign. Is that normal? Would be this campaign again open if I beat the ones above it ? If I can't choose this campaign which seems locked now, I can't reach the atlantic convoy campaign and I think , I can't play the last one, too. Any ideas ? What have I done wrong here ?

It's completely normal.
It's because at that point in the game the campaign splits/branches out, and you must choose one route/branch OR the other, and you chose the Mare Nostra route/branch.
When I get there, Im staying in the Atlantic, no way am I gonna try and squeeze my big butt past Gibraltar, especially with the IRAI mod!!!

try going back to a save point before you made your decission

I thought using sillentotto makes you lose all of your upgrades. Right?

There's nothing wrong but you can't turn back time, you cannot start a campaign that occurs earlier in the war than your character currently is in...