The problem is that the number of fields in the Energy+.IDD file is not sufficient for the IDF Editor (it is not an issue for EnergyPlus itself). You can edit the Energy+.IDD file manually using a text editor to add fields to what ever object is causing a problem by following the pattern in the IDD. Make sure you have a comma after each intermediate field and a semicolon only after the last field. The original IDD file has the Controller:MechanicalVentilation ends with:
A146,\field Zone 48 Name
\type object-list
\object-list ZoneAndZoneListNames
\note A zone name or a zone list name may be used here
A147,\field Design Specification Outdoor Air Object Name 48
\type object-list
\object-list DesignSpecificationOutdoorAirNames
A148,\field Design Specification Zone Air Distribution Object Name 48
\type object-list
\object-list DesignSpecificationZoneAirDistributionNames
A149,\field Zone 49 Name
\type object-list
\object-list ZoneAndZoneListNames
\note A zone name or a zone list name may be used here
A150,\field Design Specification Outdoor Air Object Name 49
\type object-list
\object-list DesignSpecificationOutdoorAirNames
A151,\field Design Specification Zone Air Distribution Object Name 49
\type object-list
\object-list DesignSpecificationZoneAirDistributionNames
A152,\field Zone 50 Name
\type object-list
\object-list ZoneAndZoneListNames
\note A zone name or a zone list name may be used here
A153,\field Design Specification Outdoor Air Object Name 50
\type object-list
\object-list DesignSpecificationOutdoorAirNames
A154;\field Design Specification Zone Air Distribution Object Name 50
Following this pattern, replace the semicolon on the A154 line with a comma and keep adding fields until you get to 70 fields or so, which would look like:
A209,\field Zone 69 Name
\type object-list
\object-list ZoneAndZoneListNames
\note A zone name or a zone list name may be used here
A210,\field Design Specification Outdoor Air Object Name 69
\type object-list
\object-list DesignSpecificationOutdoorAirNames
A211,\field Design Specification Zone Air Distribution Object Name 69
\type object-list
\object-list DesignSpecificationZoneAirDistributionNames
A212,\field Zone 70 Name
\type object-list
\object-list ZoneAndZoneListNames
\note A zone name or a zone list name may be used here
A213,\field Design Specification Outdoor Air Object Name 70
\type object-list
\object-list DesignSpecificationOutdoorAirNames
A214;\field Design Specification Zone Air Distribution Object Name 70
\type object-list
\object-list DesignSpecificationZoneAirDistributionNames
I have been using EnergyPlus 8.3 after upgrading those files. I have a Energy+.idd that fixes that issue with that object that you can download here. The prototype building models can be found on energycodes.gov .