If a non-ZIP file is uploaded to DMS, the user is presented with a rather generic java-exception error message as javascript alert pop-up:

"java.io.IOException: negative seek offset"

(see attached screenshot)

This is confusing to editors (i.e. any person who would upload a non-ZIP file in the ZipUpload dialog will also not understand the current error message)

Preferred Solution:

Show an error-message of the form:

"The file you uploaded ("samplenonzipfile.pdf") could not be read as a ZIP file. Please check your file."