This situation might occur if the Point Type Description and Parameter Description properties on a point contain custom descriptions. When you retrieve the event log from the ROC, the PointNumberDescription and ParameterDescription columns might not contain the expected values; instead they might contain UNKNOWN, or default values.
When the driver retrieves an event record from the ROC, it first decodes the event record to determine the point type and parameter from the record. It then searches the points that are attached to the scanner, to locate a point with the same point type and parameter values as the event record. If it finds a match, it takes the point type description and parameter description information from the point and puts it in the ClearSCADA event record.
If the driver does not find a match, it then searches a table that contains the known point type and parameter information from the ROC Plus Protocol Specification manual. If the driver cannot find a match in this table, it is unable to add the descriptive information to the ClearSCADA event record, which is why you might see UNKNOWN.
If the point in which the custom descriptions exist is attached to a different scanner to the scanner for which the driver is retrieving the event log, you might also see UNKNOWN, or default values.
This compromise was implemented due to the fact that triggering a search of all of the scanners, and all of the points in the system for a match on each event record is very inefficient, especially with large systems.