I have also had this error after finishing a first patrol. It is attributed to upgrading your boat prior to commencing your first patrol although I didn't do this. The cure is to make a save just prior to docking and if the error rears it's ugly head, just reload that save and dock again and the error normally disappears. I have never had it happen to me in subsequent patrols though.
Nemo
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"I'm afraid there is no disguising the fact that King's obsession with the Pacific and the Battle of Washington cost us dear in the Battle of the Atlantic".
Sir John Slessor GCB, DSO, MC, DL
AOC-in-C Coastal Command RAF
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