Hi,
Maybe the server is configured to force not to display error messages. The error should be logged in the PHP error log file of the server. So you can check in there (you might need to ask your hosting provider support how to access it if you don't know how or if you don't have access to it).
Also, in the past few days, I actually made a patch to fix a fatal error in some rare cases with the modules edit page. Without the error message it's possible your problem is different, but there is a possibility it is the same issue. So download again the install package of the 6.1.1 on our website and install it on yours. It will add the patch. It might fix the problem.
Otherwise, maybe it would be possible to figure out something if I could look directly at the problematic page. So, if the patch doesn't work, please provide a backend access and instructions to reproduce the problem via our contact form and I can look into it.
www.hikashop.com/support/contact-us.html