Hi, Welcome to Subsim
the cause of the problem you're facing is that you saved while at sea and where around ships.
its and old SH3 Stock Bug aka Corrupt save
the career is as good as lost and you'll have to start over (again
)
its always adviced to avoid saving while at sea, return to base instead if a RL issue cuts in.
but if you really want to save at sea make sure:
-your not close to land
-there are no ships nearby
-your submarine is surface
just to lower the risk of the save file going corrupt.
HunterICX