The problem is solved :D

In the script, I've opened the connection some times, but I've not closed the session.
In TaskManager WinSCP.exe is running many times.

I dispose the session now at the end of the script and anything works great.

Martin, thanks for your fast reply.

Thanks for your report.
I have sent you an email with a debug version of WinSCP to address you have used to register on this forum.

Dear Sir or Maddam,

I'm using the .NET assembly in Powershellscript to exchange files between a Windows Server 2008R2 an 2 Unix machines via SCP/SFTP.
First I get the files from a Unix machine to W2k8R2 via SCP. Later they will be putted on a HP-UX machine via SFTP.

If I run the script manually, the script completes without any errors. If I run the script via Scheduled Tasks (The local admin is defined to run the task), a error will be created in Event Viewers Queue "Application" -look for Error below-.
In both cases, the filetransfer works great, so I don't know why the error is shown.

Queue: Application
ID: 1000
Source: Application Error

Name der fehlerhaften Anwendung: winscp.exe, Version: 5.5.0.3839, Zeitstempel: 0x00000000
Name des fehlerhaften Moduls: winscp.exe, Version: 5.5.0.3839, Zeitstempel: 0x00000000
Ausnahmecode: 0xc0000005
Fehleroffset: 0x002bf2a0
ID des fehlerhaften Prozesses: 0xb88
Startzeit der fehlerhaften Anwendung: 0x01cf141a050e0306
Pfad der fehlerhaften Anwendung: C:\Program Files\WinSCP\winscp.exe
Pfad des fehlerhaften Moduls: C:\Program Files\WinSCP\winscp.exe
Berichtskennung: 4382d468-800d-11e3-8497-00155d8e1904

I didn't found any troubleshooting information. It would be great, if I get help asap.

L. Ellerkamp