In case you have installed one of trial skins for DNN, it may happen that, once the trial expires, changing skin again becomes impossible.
In these cases, when you try to change the skin back to another, the site keeps coming back to the expired trial theme.
Apparently a piece of script in trial skins is preventing the page to change.
To solve this, please edit layout files (.ascx, as inner.ascx or home.ascx) and remove:
This should be the last line in the file.
Bind is working towards releasing a fix to this issue in the next version.