Here is the GetLastErrorMsg function from my answer:

Function ulong GetLastError( &
   ) Library "kernel32.dll"

Function ulong FormatMessage( &
   ulong dwFlags, &
   ulong lpSource, &
   ulong dwMessageId, &
   ulong dwLanguageId, &
   Ref string lpBuffer, &
   ulong nSize, &
   ulong Arguments &
) Library "kernel32.dll" Alias For "FormatMessageW"

public function string getlasterrormsg ();// -----------------------------------------------------------------------------
// SCRIPT: GetLastErrorMsg
//
// PURPOSE: This function gets the most recent system error.
//
// RETURN: The error message
//
// DATE       PROG/ID  DESCRIPTION OF CHANGE / REASON
// ---------- -------- -----------------------------------------------------
// 12/31/2021 RolandS  Initial coding
// -----------------------------------------------------------------------------

Constant ULong FORMAT_MESSAGE_FROM_SYSTEM = 4096
Constant ULong LANG_NEUTRAL = 0
String ls_buffer, ls_errmsg
ULong lul_error

lul_error = GetLastError()

ls_buffer = Space(MAX_PATH)

FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, 0, &
   lul_error, LANG_NEUTRAL, ls_buffer, MAX_PATH, 0)

ls_errmsg = "Error# " + String(lul_error) + ": " + ls_buffer

Return ls_errmsg

end function

Register your app :

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\EventLog\Application\MyAppName

EventMessageFile REG_EXPAND_SZ %SystemRoot%\System32\wshext.dll
TypesSupported   REG_DWORD     0x0000001f (31)

External Functions:

Function longptr RegisterEventSource ( &
   longptr lpUNCServerName, &
   string lpSourceName &
   ) Library "advapi32.dll" Alias For "RegisterEventSourceW"

Function boolean ReportEvent ( &
   longptr hEventLog, &
   uint wType, &
   uint wCategory, &
   ulong dwEventID, &
   longptr lpUserSid, &
   uint wNumStrings, &
   ulong dwDataSize, &
   string lpStrings[], &
   ulong lpRawData &
   ) Library "advapi32.dll" Alias For "ReportEventW"

Function boolean DeregisterEventSource ( &
   longptr hEventLog &
   ) Library "advapi32.dll"

Instance Variables:

Constant UInt EVENTLOG_SUCCESS = 0 // Success event
Constant UInt EVENTLOG_ERROR_TYPE = 1 // Error event
Constant UInt EVENTLOG_WARNING_TYPE = 2 // Warning event
Constant UInt EVENTLOG_INFORMATION_TYPE = 4 // Information event

Function:

public function boolean writetoeventlog (unsignedinteger aui_type, string as_message);// -----------------------------------------------------------------------------
// SCRIPT: WriteToEventLog
//
// PURPOSE: This function writes a message to the event log.
//
// ARGUMENTS: aui_type   - Use one of the instance constants:
//                         EVENTLOG_SUCCESS
//                         EVENTLOG_ERROR_TYPE
//                         EVENTLOG_WARNING_TYPE
//                         EVENTLOG_INFORMATION_TYPE
//            as_message - The message text
//
// DATE       PROG/ID  DESCRIPTION OF CHANGE / REASON
// ---------- -------- -----------------------------------------------------
// 12/31/2021 RolandS  Initial coding
// -----------------------------------------------------------------------------

Longptr ll_EventLog
String ls_msgtext[], ls_ErrorMsg

// log the message
ls_msgtext[1] = as_message

ll_EventLog = RegisterEventSource(NULL, "MyAppName")
If ll_EventLog > 0 Then
   ReportEvent(ll_EventLog, aui_type, &
      0, 0, 0, 1, 0, ls_msgtext, 0)
   DeregisterEventSource(ll_EventLog)
Else
   ls_ErrorMsg = GetLastErrorMsg()
   WriteToLogFile("RegisterEventSource Failed: " + ls_ErrorMsg)
   Return False
End If

Return True

end function

Hi, 

I think this would be a good place to start: https://docs.microsoft.com/en-us/windows/win32/eventlog/event-logging-reference 

but ... with a little bit of luck, Chris has already build in similar functionality in his STD classes?

regards.

LMGTFY:

https://www.google.com/search?q=powerbuilder+use+windows+event+log