I don't think we have such a known issue. Could you please try the following:
1. Check the App_Data permissions. It is possible that you do not have a write access to the files in it. The Asp.Net worker process should have this access. You may check with what user your application is running on.
2. Empty the log fie (copy its content to some other file, for example Sitefinity_old.log).
Let me know if this helps.
All the best,
the Telerik team