[CentOS] YUM error "can't create transaction lock"

A short while ago I reported a network interruption while 
performing a YUM update on a server.  A check of the logs as 
recommended by a list member indicated that the update process had 
succeeded.  However, I am now encountering the following problem on 
that same server and my nastily suspicious mind is trying to tell 
me that the previous event and this situation are somehow related.

> Downloading Packages:
> Running Transaction Test
> Finished Transaction Test
> Transaction Test Succeeded
> Running Transaction
> warning: waiting for transaction lock
> error: can't create transaction lock


I have googled for this error and have come across a web site 
devoted to it, but for Redhat's rpm and up2date managers only.  
There is evidently a lock file or database entry that is preventing 
yum from proceeding but I am not sure that the information that I 
have found applies to yum and I am unable to clear the lock 
manually.

After following all the recovery steps I reach this point:
> /usr/lib/rpm/rpmdb_dump Packages-ORIG | \
>     /usr/lib/rpm/rpmdb_load Packages
> rpm -qa
> rpm --rebuilddb
> warning: waiting for transaction lock

Any assistance with this problem is gratefully accepted.  I am a 
digest subscriber so the favour of a direct reply is appreciated.

Regards,
Jim

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