Connection terminated abnormally (SQLA12.0.4086)

Hi,

one of our customers reported a problem with our application. We checked the console log and found this messages:

...

I. 27.10 08:51:54. Verbindung wurde abnormal beendet, Fehlercode 121

I. 27.10 08:51:54. AppInfo des getrennten TCPIP-Clients: HOST=WIN2K8TS;OS=Windows NT 6.2 Build 9200 ;PID=0x8e4;THREAD=0x7b4;EXE=X:\TelApp.exe;VERSION=7.0.4.3541;API=ODBC

...

Translated that would be something like this:

Connection was terminated abnormally, error code 121

AppInfo of the disconnected TCPIP-client: ...

Any idea where I could look up this error code?