Error saving xml DARK theme

I’m running eM Client version 7.0.30068.0 on Windows 7 x64 and get an error when trying to save a theme by choosing Menu>Tools>Settings, selecting Appearance>Themes, and clicking on Advanced then Save current theme as … followed by clicking on the Save button in the _Save as _window.

The error reads:  An error occurred when saving the theme. Saving failed due to the following error: “There was an error generating the XML document.”.

This happens on most of the themes but not ALL of them - i.e. DARK theme does not save and gives this error but the SYSTEM theme saves fine.  BORDEAUX theme also gives this error.

Any ideas?