Error when compiling theme in Eclipse

Hello,

I want to compile my theme because I want now to have my app in production mode.
When I press “compile theme” in the Eclipse toolbar the following error appears:

Error compiling theme:
Java.lang.ClassCastException - org.eclipse.core.internal.resources.FIle cannot be cast to org.eclipse.core.resources.IFolder

Also, when I request Eclipse to Clean the project a similar error appears which is the following:

Errors occurred during the build.
Errors running builder ‘Addon Styles Builder’ on project ‘TimeTracker’.
org.eclipse.core.internal.resources.File cannot be cast to org.eclipse.core.resources.IFolder

Any clues what is going on?

Thanks in advance

FYI: TimeTracker is the name of my app

Screenshot of error
16620.png

Fixed the same issue by deleting
.DS_store
files from WebContent directory and subdirectories. It wasn’t ‘compile theme’, but ‘clean project’ for me…
See
https://dev.vaadin.com/ticket/12539