Below my solution

Guide: https://community.microfocus.com/borland/tm_art/w/knowledge_base/22848/classifying-tm-art-workbench-script-runtime-error-as-availability-or-accuracy-error-in-tm-art-central

Steps:

• open file .ltz with Silk Performer
• Settings -> Active Profile -> Replay -> Simulation -> Errors tab
• Click the Add... button.
• Select a module and a severity and the list of predefined error codes will appear in the table.

For example, select "BMC TM ART - HTTP" as module and "error" as Severity. In the list of error codes, you will find the code "500" and its error description "internal server error". Below is a screenshot of some error codes for the WinSock module.

• Select the new severity
• Save and reload file .ltz