...
Note: If the Optimize Structure Read parameter is enabled, browsing also displays individual elements of structured variables. If you want to read Rockwell STRINGs (which are essentially structures with DINT and SINT ARRAY items, see the following screenshot), you must check Auto can select the appropriate STRUCTURE type item in the browsing dialog to set the Attribute Type to NONE/AUTO and not to STRUCTURE(in the screenshot AlarmRspMsg.Path).
Atribute type - the type of attribute. In the case of standard addressing, it is necessary to enter a specific type. In the case of symbolic addressing, it is possible to leave the type of the attribute as NONE/AUTO (autodetect), since proprietary Rockwell messages contain both the value and the attribute type. An exception is if the I/O tag is write-only - then the attribute type must be specified.
...