Undefined variable: LANG in ext.cm_template_editor.php on line 156

I was using Template Editor v1.0.0 and Edit_Area 0.7.1.1 under EE 1.6.4 just fine until today. I did the following:

Updated EE to 1.6.7 Updated Edit_Area to 0.7.2.3 Disabled Template Editor v1.0.0 Installed CM Template Editor 2.2.0

Now, I get this error when attempting to submit configuration settings:

Undefined variable: LANG in ext.cm_template_editor.php on line 156

Any idea what’s happening here?