Nextend plugin install failed

If you see this error message during installation:
Plugin could not be activated because it triggered a fatal error.
It seems like that the WordPress installer can not write /wp-content/plugins
Please install manually the following library plugin: wp-contents/plugins/nextend-accordion-menu/nextend/ => Then you can activate this plugin!”

Then just follow the instruction, install the file seperately. You can find it inside Accordion menu's installer, inside the Nextend folder.