MarketPress Plugin Causing "Service Unavailable" Error Message

I'm having an interesting problem using the MarketPress plugin. Currently running WordPress 3.8.1 MultiSite.

When the plugin is active, all sub pages under /services/ displays a "Service Unavailable" error message. All other sub folders work fine. After deactivating the plugin, the error goes away on the pages but redirects to the home page; refreshing the permalinks fixes the redirection problem.

I have tried changing the store directory configuration within the plugin, deactivated all other plugins, and tried a few other themes; no luck.

Anyone else having this problem?