Release : 8.6
Component : Gen Workstation Toolset
All CALL EXTERNAL error return codes start with 3 and correspond to Gen TIRM3nnE errors.
A full list of TIRM3nnE messages can be found under the Runtime Messages > Common Runtime Messages TIRM000E - TIRM599E section of the Gen techdocs i.e. starting here for 301 with TIRM301E.
The error codes are also listed in the file tirabrt.h found in the Gen installation directory "%Gen86%\Gen"