I too faced similar situation where in taking log backup to disk throws error message as BACKUP detected corruption in the database log. Following are the things that I have done and it worked fine for me

1) Took full back of database

2) Run checkdb on database

3) Backup log with truncate_only options

4) Took again full back of database

5) Run backup log to disk and it work working fine.

I guess this is due to some VLogs problem.