What does this warning mean?

["Mark Hull-Richter" <mhullrich gmail com>]

When I try to open various files from the command line, although not all of them, I often get this error message:

(acroread:10552): Gtk-WARNING **: Unable to locate theme engine in module_path: "bluecurve",

That was from the Acrobat Reader, but I also get it from Open Office, the image viewer and a few others.

What does it mean and how do I get rid of it?

Thanks.

mhr