Bug 118644 Hint for Date Time Parameters
The hint you give for date time parameters (Please enter date ... pattern: MM/DD/YYYY ....) is only true if the date is unformatted. If you apply a format, you must enter it according to it. So it's quite confusing!
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
{
			if ( value == null || value.length( ) == 0 )
			{
				return ERROR_MSG_CANNOT_BE_NULL;
			}
		}
		if ( canBeBlank( ) )
		{
			if ( StringUtil.isBlank( value ) )
			{
				return null;
			}
		}
		else
		{
			if ( StringUtil.isBlank( value ) )
			{
				return ERROR_MSG_CANNOT_BE_BLANK;
			}
		}
		try
		{
			if ( DesignChoiceConstants.PARAM_TYPE_BOOLEAN.equals( getSelectedDataType( ) ) )
			{
				DataTypeUtil.toBoolean( value );
			}
			else if ( DesignChoiceConstants.PARAM_TYPE_DECIMAL.equals( getSelectedDataType( ) ) )
			{
				DataTypeUtil.toBigDecimal( value );
			}