Help

Hi guys, I am after a little help with sh3 from someone.
I am playing 1939 with type xxi Sub. I only have a couple of mods loaded but don't think that is affecting my progress.
Basically, every time I finish 1st patrol docking at Lorient, It says "I have died" and I have to start a new campaign. This has happened 3 times now, and I can not find anything related to my problem.
Is it the sub that I am using causing this or what. I sunk plenty ships, and have avoided all attacks from enemy.:k_confused.
Hope you can help ????
Good hunting, johnboy1958