How to manual reinstall Windows XP Telephony service (TapiSrv) that fails to start with Event ID 7023 (cannot find file specified)?

Question

After using the XPlite tool the Windows Telephony service is no longer installed on our Windows XP Professional SP3 installation.

I was partly successful in manually reinstall the missing Telephony service, by:

1. retrieve the missing TapiSrv.dll file from http://originaldll.com/file/tapisrv.dll/2345.html
2. recreate the service with the command sc create TapiSrv binpath= "C:\WINDOWS\System32\svchost.exe -k netsvcs" type= share displayname= "Telephony" error= normal start= demand depend= "PlugPlay/RpcSs"

A manual start of the "Telephony" service fails with Event ID 7023:

The Telephony service terminated with the following error: The system cannot find the file specified.

How can I start the Windows XP Telephony service again without re-installing the OS or restore from a backup?

Answer 1

After adding this registry key to HKLM\SYSTEM\CurrentControlSet\Services\TapiSrv\Parameters with name ServiceDll of type "expandable string value" (REG_EXPAND_SZ) and value %SystemRoot%\System32\tapisrv.dll, the "Telephony" service is able to start.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TapiSrv\Parameters]
"ServiceDll"=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,\
  00,74,00,25,00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,\
  74,00,61,00,70,00,69,00,73,00,72,00,76,00,2e,00,64,00,6c,00,6c,00,00,00