User rights for logging

Hello,

I have ad a windows domain account to a custom windows service.

I also add this user to local security policy ->log on as service. Everything works fine, the service is running.

Now my question:

The service normal writes log files to folder c:\programdata\company\...

The logs are written if the user is local admin, if I remove the user from local admin group, no logs are in the log folder.

Which permission did I have to grant for this ad service account user, to write the logs without give them local admin rigths?

I hope somebody can help me,

Thanks Horst MOSS 2007 Farm; MOSS 2010 Farm; TFS 2010; IIS 7.5