Make sure you have enough disk space. Also, verify that you have full access to the build directory and the webpages subdirectory. You must have read, write, create, and delete privileges to the build directory.

If you have version 7.1.7, then this error can be reported because a file is missing from JExpress' distribution. A work-around for this version is to define an Image filename on the Appearance panel/tab and then rebuild your project.