There is a minor typo mistake in the English (UK and US) language pack in Configure Screen Scheme page (Administration -> Issue Fields -> Screen Schemes -> Click on "Configure" link).

To activate this screen scheme, map it to one ore more issue types using an Issue Type Screen Scheme and then associate the Issue Type Screen Scheme with one or more projects.

There is an extra "e" at the word "or".

The correction should be made at this property in there language pack properties file: admin.issuefields.screenschemes.configure.instruction2