Hi Reimer,
More specifically to Jason's answer, the error should be a Windows *operating system* error code (which does turn out to be frequently a Winsock error error code when working with networks: Windows Sockets Error Codes (Windows) )
In this specific case however, it is a regular System Error code: System Error Codes (Windows)
You can always see which system code it is by using 'net helpmsg #' at a Command Prompt:
C:\>net helpmsg 121
The semaphore timeout period has expired.
You can then use this information to search for further issues, for instance on Microsoft's website about this error (ERROR_SEM_TIMEOUT) and network adapters: http://support.microsoft.com/kb/325487
Regards,
Jeff Albion
SAP Active Global Support