Problem - This account register is read-only

[John Deakin]

Hope you can help.

When I open Gnucash I get a warning box with the header as in the e-mail 
subject. The text in the box is:

"This account may not be edited.  If you want to edit transactions in 
this register, please open the account options and turn off the 
placeholder checkbox."

I cannot find the account option to turn off the placeholder checkbox. 
What am I missing?

regards,
John