Hyperion: Planning PSU application breaks Financial Reporting Studio

Our team had applied a Hyperion Planning PSU in DEV to try and resolve a report issue, but they reported that they started receiving an error in Financial Reporting Studio starting with "HARSnapin Initialize() Error -2147467259 - ; nested exception is: java.rmi.UnmarshalException: error unmarshalling return" when they tried to open any report.  The key here was the PSU that was deployed, as My Oracle Support note 1518423.1 was applied to "refresh" Financial Reporting Studio but if there wasn't a new PSU deployed note 1311069.1 could have applied where a file was corrupted on the server that needed replacing.