[GNC] Cannot change preferences

[Ken Heard]

I have been using GnuCash since 2009.  Twice every year I need to 
transfer my account file from one desktop to another.  I never had any 
trouble opening GnuCash after each such transfer until now.

Early on in my use of GnuCash I changed the accounts separator from the 
colon (:) to the back slash (\).  Since that change I use the colon in 
quite a few account names, currently numbering about fifty..

When I tried to open my account after the most recent transfer, a window 
appeared saying the following.

	The separator character ":" is used in one or more
	account names. [Actually about 50 accts.]

	This will result in unexpected behavour.  Either change
         the account names or choose another separator character.

I would like to do one or the other, but the GnuCash Preferences window 
is locked.  I can open it on the monitor but cannot make changes to 
*any* of the preferences.

The version of GnuCash which I want now to use GnuCash is 2.6.15, the 
latest one available with Debian Stretch.  I am not sure what version 
was the previous computer, except to say that it was likely the latest 
version available with Debian Wheezy.

I would appreciate receiving information on how to fix this problem. I 
did try to find the location of the file containing the selected 
preferences but was unsuccessful.

Regards, Ken