Geotransformation is not valid

[LT]

Hi All,

I'm trying to find the area of my Denver, Colorado polygons in kilometers (km) and I think my data is in Decimal Degrees, so I need to project it before using calculate field to calculate the area. 

My data properties say the following:
Data Type: Shapefile Feature Class
Shapefile: C:\foo.shp
Geometry Type: Polygon
Coordinates have Z values: No
Coordinates have measures: No

Geographic Coordinate System: GCS_WGS_1984
Datum:  D_WGS_1984
Prime Meridian:  Greenwich
Angular Unit:  Degree

My specific questions are:

1. I think this means my data is in decimal degrees and I need to project it to get an accurate area measure in km.  Does this sound correct?



2. I believe an appropriate coordinate system would be:

NAD_1983_HARN_StatePlane_Colorado_Central_FIPS_0502_Feet

My source of coordinate system selection is from here:
http://www.denvergov.org/?TabId=426422

http://www.spatialreference.org/ref/?search=Colorado
Does this sound correct?


3. The project tool requires a coordinate system transformation and I selected NAD_1983_To_WGS_1984_5.  Does this sound correct? 

I based this selection on this source: http://blogs.esri.com/esri/arcgis/2009/05/06/about-geographic-transformations-and-how-to-choose-the-...

which says:
HowTo: Determine which NAD_1983_To_WGS_1984 transformation to use--
NAD_1983_To_WGS_1984_1 �?? for the entire North American continent.
NAD_1983_To_WGS_1984_2 �?? for the Aleutian islands.
NAD_1983_To_WGS_1984_3 �?? for Hawai�??i.
NAD_1983_To_WGS_1984_4 �?? superseded by _5; this transformation method should no longer be used!
NAD_1983_To_WGS_1984_5 �?? for the 48 contiguous United States.
NAD_1983_To_WGS_1984_6 �?? for the Canadian province of Quebec.
NAD_1983_To_WGS_1984_7 �?? for the Canadian province of Saskatchewan.
NAD_1983_To_WGS_1984_8 �?? for the Canadian province of Alberta.


I get an error when I run the Project (Data Management) tool. 
Here's a picture of how I filled in the Project GUI: http://screencast.com/t/ARKUS3wQdf
This is the error I get:
ERROR 000151: The geotransformation(s) is not valid.  Failed to execute (Project). 
Any ideas why this may be happening?

Thank you for your help!

[LT]

Oops-- I got rid of the error by switching to

NAD_1983_StatePlane_Colorado_Central_FIPS_0502

instead of

NAD_1983_HARN_StatePlane_Colorado_Central_FIPS_0502

So you can ignore question #4.  However my first three questions still remain. 

Thanks again.