Project properties: The currently displayed page contains invalid values

I clicked on Project > Properties and then selected the PMD tab. I get the following error message:

Title: Could Not Accept Changes
Message: The currently displayed page contains invalid values.

The content section of the window is blank.

I tried uninstalling and re-installing the plugin and I get the same error.

Are there some property files I can remove to workaround this problem.

I am running Eclipse 2019-12 (4.14.0) build id 20191212-1212 with PMD Plug-in version 4.10.1.v20200207-1909 on Windows 10 version 1903. I am running Eclipse on HotSpot 11.0.4.

In Eclipse's Error Log, I see 2 errors: Error instantiating a rule and Problems occurred when invoking code from plug-in: "org.eclipse.jface". The latter has an exception ClassNotFoundException. The message complains about a class for a custom Java rule I wrote. I removed the custom rule from my PMD ruleset XML file and I can now see the property page.

How do I add my custom class so that the PMD plugin can use it? I tried "Select a working set..." on the property page but that did not seem to work.

Start at the Eclipse Project > Properties > PMD tab flow and inspect the Error Log entries for “Error instantiating a rule” and the ClassNotFoundException. Reproduce with the custom rule in the ruleset, then verify that the custom class can be resolved and the PMD property page displays its contents without the invalid-values error.