I am trying to migrate liferay from version 7.0 to 7.4. I am able to click on Options on right hand corner of each portlet. But, when I click on look and feel configuration Option a blank pop up appears. No contents are shown. This issue not only happens with my custom theme but also with classic theme.
I tried setting some properties like look.and.feel.modifiable=true in portal-ext.properties file. And also I tried logging in with admin user. No luck. I am not sure if I have to change any permissions or should I modify any ftl files.
Thanks for your help.
I had the same problem, try to add: "javax.portlet.version=3.0" in the main portlet java with all the other properties. In my case work.