KB-XXXX Plugin fails to deploy with error in app server log, "Cannot open JAR file for reading"

Symptoms

A plugin fails to deploy, and the application server log shows the following error:

[Appian Plugin Hot Deploy] ERROR com.appiancorp.plugins.LoggingPluginEventListener - Failed to load Plug-in '<Plugin Name>.jar' (<Plugin Name>.jar) version 0.0: 'Cannot open JAR file for reading: <Path to plugin>/<Plugin name>.jar'

Causes

Cause 1

The plugin does not have the correct permissions or ownership to be executed by the user running Appian.

Cause 2

 The plugin files are corrupt.

Actions

For cause 1

Ensure that the plugin has plugin the correct permissions and ownership to be executed by the user running Appian.

For cause 2

Re-import the original plugin into Appian.

Affected Versions

This article applies to all versions of Appian.