Short post; still digging. May turn this into general a Java error page.
Had the opportunity to deploy an application that has a combination of ASP and Java components. The setup documentation wasn't the best, so had to prowl around the Internet for solutions.
The error occurs when moving a mouse over a JavaScript function that invokes a Java component. It includes a popup in IE (unless you've disabled them, in which case you get an error icon in the lower-left corner), with an 'object not found' notification.
In this case, the missing piece of documentation is including an S/MIME type with an extension of “.inc” and a MIME type of “Java”.