Start a new game and build a stop, it says "That would exceed your credit limit."
So, I can do nothing.
I also encounter this problem. Maybe that's also the reason why the AIs don't work properly.
Thank you for that bug report - I have been able to reproduce. I am looking into that now; will report back soon. Thank you very much for testing it!
Edit: Problem found: it was no more than an errant semi-colon, of all things. And that does fix the AI, too (when I tried it, the passenger AIs worked fine, but the goods AIs had some problems working out how to connect a railway with a dock so as to make money, although I suspect that a similar problem is encountered in Simutrans-Standard). The fix will be available in the next minor release, which should be coming soon.
Thank you.
And one more, credit limit doesn't affect raise/lower land tool.
I can always raise/lower without money.
Aha, thank you for spotting that! I will have a look into that.
Edit: Fixed in 2.1.