Possible conflict with Error Reporting custom 403 and 404 pages

I'm having a strange problem with this great module.

I have a rule using Path Rules set up like so:

1. If path is equal to "my-target-path"
2. Redirect user to "user/[user:uid]/new-path"

This works perfectly when the user visits "my-target-path".
However, if the user tries to access a url that results in a 404 or 403 error (which I have set to display different nodes via 'admin/settings/error-reporting') the following error occurs:

Fatal error: Unsupported operand types in C:\Inetpub\wwwroot\drupal\includes\common.inc on line 1593

This doesn't happen if 404 and 403 are left as their default pages. It also doesn't happen if the Token module is disabled.

I've narrowed this down to this module by disabling all other modules -- any direction on troubleshooting this further would be much appreciated!!