Exactly what it says, all logical log files are in use, so there are no empty ones. No empty VLFs = no shrink.
Check log_reuse_wait_desc in sys.databases for why the log is not being reused.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability