Shapefiles, rasters, computer-aided design data, and geodatabases display 'Unknown' as the coordinate system even when the data has a defined coordinate system. However, the coordinate system for coverages does display properly.
In ArcCatalog, browsing the Coordinate Systems directory and attempting to open one of the .prj files results in the following error message:
"Failed to create the spatial reference system from the specific prj file."
The decimal separator in the regional settings does not match the locale of the machine.
Does the Decimal symbol value match the set locale? For example, English (United States) uses a period for the decimal symbol value. Spanish (Modern Sort) uses a comma for the decimal symbol value.