GIMP cannot open files that contain unicode charaters in their paths when called by an external application (like Windows Explorer).
Steps to reproduce:
1. Create a file with a name "тестテスト.jpg" or place any of your image files in a folder named "тестテスト".
2. Double click on the file or (if GIMP is not your default application) right click on it and choose "Edit with the GIMP" from the contextual menu.
What you get is an error message:
JPEG image Message
Could not open <lots of ???.jpg> for reading: invalid argument.
GIMP Message
Opening <lots of ???.jpg> failed: JPEG image plug-in could not open image.
I already opened a bug in http://bugzilla.gnome.org/show_bug.cgi?id=481373
but GIMP developers say it might be the problem with this tool.