Hello. I'm having the same issue. Fresh install of tekkit, both client and server, and I cannot open the minecart chests at all. I have tried playing with the config file for railcraft but it hasn't proved successful. I did try disabling railcraft just to see if it solved the issue and it does seem to allow me to open the chests.
I would really like a solution to this problem. I am looking forward to playing with railcraft but this problem is going to stop me from doing so.
Thanks.
Edit: Also would like to add I'm not using permissions.