From the sound of the error, there's corruption in the transaction log. Drop the affected databases and reconfigure log shipping for those DBs from scratch.
Also, do some checks of the IO subsystem on that server, look for any errors, misconfigurations, warnings or alerts. Corruption is typically an IO subsystem problem.
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