Bernd,
Try taking a look at the logging level for SAP and the Server on BC. To do this, go the Settings and logging in the Administrator and select the SAP from the Component drop down. I believe that a 7 or higher significantly increases the amount of logging on BC.
For you immediate problem, starting and stopping BC usually frees up the file and you should be able to delete it then, probably via a built in delete or a custom job that you could schedule.
As far as the log getting really big, that seems odd that it would do that. I would venture to say that you probably have your logging setup to be “verbose”
Good luck,
ajandja
#Integration-Server-and-ESB#B2B-Integration#webMethods