Unable to install Labeler

[Reid Harrington]

I am unable to manually install Labeler in our offline instance of Confluence 5.9.1, I have tried all 4 versions available and get the same error each time:

"An error occurred during installation. Refer to the logs for more information"

"Failed to install add-on plugin_......_labeler-1.1.3.jar"

Any help would be appreciated.