This is only tangentially related to eWallet.  eWallet is unable to access a Windows theme; your Windows themes may have become unavailable (are "Visual Styles" disabled in eWallet shortcut?) or corrupted somehow.

Close eWallet on the PC.  If you right-click the Windows desktop background and choose "Personalize", can you select any of the more Advanced Aero themes, or does it error out? 

If you are still having trouble, and you are running Windows 7, try this:

    http://windows7themes.net/auto-repair-windows-7-with-microsofts-fix-it-center.html
      Choose the "Aero" tool.