Logfile error

Hi there,
i have a extern winscp-script, opened via a batch file.
i'm opening with the following parameters:

WinSCP.com /script=scpscript.txt /log=log.txt

in my logfile, the first lines are:

batch on
confirm off
Error occured during logging. It's been turned off.
Can't open log file 'log.txt'.
Searching for host...
Connecting to host...
Authenticating...


there is an existing file called log.txt in the same folder as the batch and the winscp script. forgot anything?
ps: read doc and faq a few times before but still without an idea.

thanks

Crosspost.