Earlier Log files keep getting skipped

SQL_Dude

We have been using SQL Backup for log shipping for 4 months now.  Every week we reach a point where the restore job starts failing.  I am able to track the error an invariably it always turns out that an earlier log file needs to be restored first.  I am not sure how the earlier log file is getting skipped and find it is easier to delete the log shipping jobs and restart the whole process from the beginning.  I tried to download the log shipping monitoring tool but it will not install -probably I do not have enough rights on the server.  How can we keep the transaction logs from getting out of sequence?