Solution:
Review the ITAMDataImporter<date>.log file
If it contains the following error:
5/4/2012 9:43:14 AM Load Importable Classes:
5/4/2012 9:43:15 AM System.NullReferenceException: Object reference not set to an instance of an object.
at UAPM_Import_Tool.Constants.getLocaleFromRegistry()
at UAPM_Import_Tool.Mapper..ctor(frmMain frm, Settings settings)
at UAPM_Import_Tool.frmMain.frmMain_Load_WithoutInjectedLogging3619502461923(Object sender, EventArgs e)
5/4/2012 9:44:09 AM ITAM Data Importer returns with Error Code: -1
Then this error is related to either a missing or incorrect 'Locale' setting in the registry.
Use regedit to view the values and keys at:
HKEY_LOCAL_MACHINE\SOFTWARE\ComputerAssociates\Unicenter Asset Portfolio Management
The Locale string should be set to value = 0 for the English culture.
If the Locale string does not exist in this location, then add it by right mouse clicking -> New -> String value.
Type Locale for the Name, then modify it with a value = 0. The registry entry should appear as: Locale REG_SZ 0