This issue comes very often. When attempting to check on the "Log file rotation enabled?" option, it gives the following error:
Setting up log file rotation ..
.. Log file rotation failed! : .. the log file /var/log/virtualmin/domain.com_access_log is already being rotated at /usr/libexec/webmin/web-lib-funcs.pl line 1427.
Saving server details ..
To address this issue we usually remove the .conf file for the website in the /etc/logrotate.d directory, however this time there is no such file for the domain name. But this issue is not about this particular case, because there tons of support requests in the issues queue and forums for the same problem and I believe it is high time for *min team to properly address this issue.